Reason #1: Bad for Search Engines (SEO)
If you want your website to appear in search engines, do not use Flash. Flash pages don't get indexed properly by search engines due to the fact that search bots simply can't read Flash content. As far as the search engines are concerned, you might as well have a website that consists of a title, some meta tags, and no other content, in other words your website is INVISIBLE!
It doesn't matter how pretty your website is or how fluid the animations are if no one will ever find it.
Nowadays, Flash can even hurt your search rankings. Many search engines have begun blacklisting websites that have meta data unrelated to the website's actual content, because such websites are regarded as being deceptive in their attempts to gain web traffic. As far as the search engines are concerned, Flash websites have keywords, but no content, which commonly results in blacklisting due to the perceived discrepancy.
Reason #2: Limited Mobile Viewing
As the iPhone, Blackberry, and other smartphones have skyrocketed in popularity and usage, more and more websites are being accessed on the go from mobile web browsers. But guess what? Most mobile web browsers have no Flash support, so they can't display Flash websites at all. Those that can (in theory) are still limited by the memory and processing power of the mobile device and will often choke on Flash websites because of their increased bandwidth and CPU demands. ( More on bandwidth and CPU demands in Reason #10 below. )
Reason #3: No Linking or Bookmarking
Every page of a Flash website has the exact same web address, or URL. In other words, no matter which page you're viewing on a Flash website, the URL is exactly the same. On normal websites, you can bookmark and link directly to specific pages using unique URLs. This makes it easy to find your way back or to share these pages with others.
Without unique URLs, it's impossible to bookmark pages, and you'd have to include click-by-click instructions to help someone else find their way to a specific page after sending them a link to your website.
Reason #4: No Back Button
Suppose someone is clicking their way through your website, finds themselves on a page they didn't mean to click to, and decides they want to go back. This is where the back button comes in on a normal website. On a Flash website, the back button is either disabled altogether, or it will take them to the website they were viewing before yours! Eventually, they'll have to figure out how to get back another way, such as by reloading the whole website and starting over. This is far from ideal and can seem quite inhospitable to your website visitors.
Reason #5: Poor Design Standards
The bells and whistles that come with Flash almost always result in gratuitous design abuse when it comes to websites. Successful webmasters understand that the Internet is a standards-based system. Navigation goes here, content goes there, a click does this, a drag does that, and so on. It's a standard user experience that shouldn't be re-invented on a whim. Most website visitors are annoyed by broken usability standards, and older or less experienced website visitors will often give up and leave. (More on usability failures in Reason #9 below.)
This isn't to say that pushing design boundaries is always a bad thing. In fact, it's the only way innovation can come about. But the ratio of "revolutionizing" design change to "senseless and gratuitous" design change leans far to the latter, and too many webmasters who try to create something unique and edgy only make their websites unusable as a result.
Nowhere is this phenomenon more prominent than with Flash websites.
Reason #6: Content Loading...
On a normal website, content is instantly viewable as each page or image downloads to the web browser. On a Flash website, however, the entire website has to download before any part of it is viewable. This is the reason 99% of Flash websites start with a loading screen.
Compare this to the old days of web video when you had to wait for the entire video to download before it would start playing.
Nowadays, streaming video is the standard, because it allows the video to play instantly while it downloads. Flash is incapable of streaming, however, so Flash websites will always behave like the old, non-streaming videos that no one misses.
Reason #7: Splash and Intro Pages
Splash pages are those annoying intro screens that you often see before clicking "skip intro" or "enter here" to access the real website. Splash pages nearly disappeared a decade ago for their inherent uselessness, but - in a step backwards for web design and usability - many Flash designers have developed a unique dependency on them. Most often, splash pages are used to give visitors a choice between viewing the Flash or non-Flash version of a website. Putting aside the utter pointlessness of having two versions of the same website, this creates an extra and unnecessary hoop for your website visitors to jump through in order to get to your content. Just ask yourself this question... "When I visit a site with a splash page and I am given the option to skip, what do I do?" - The same applies to your site's visitors.
Reason #8: Basic Text Functions Broken
On Flash websites, it's impossible to make use of basic text functions like copy-and-paste, finding text, or changing text size to improve readability. There's no right-click menu to facilitate these tasks, and keyboard shorcuts don't work with Flash. Also, since the text displayed by Flash websites is unreadable by web browsers, visitors who depend on screen readers due to vision impairments might as well be staring at a blank screen.
Reason #9: Poor Usability Standards
While most of these twelve reasons involve the usability failures of Flash websites, this section specifically addresses how Flash designers typically break or ignore standard user interface elements of the Web.
Internet users are accustomed to certain user interface elements, and they don't want to learn or adapt to anything new just to use your website. Scrollbars and buttons should look and respond in a familiar way. Navigation menus and forms should behave predictably. While most Flash designers will forego such standards for the sake of being different, time-tested usability standards will always offer a better user experience than a custom widget cooked up by a well-meaning Flash designer over the weekend.
Reason #10: Bandwidth and CPU Demands
Flash websites can bring older computers to a crawl, and they can take much longer to load with sub-broadband Internet connections. While this may only affect a small portion of your intended audience, why alienate anyone by denying them a good experience while viewing your website? Remember that if it takes too long to load, or if it runs too slowly on their computers, visitors will often leave your website before they've even seen it.
Reason #11: Dependency on 3rd-Party Plugins
Most people forget that Flash is a proprietary technology owned by Adobe. In fact, Flash websites can't even be displayed without Adobe's free Flash Player plugin. While it's generally accepted that over 90% of today's Internet users already have the necessary plugin, the rest of the population is either excluded or forced to download and install it. This may be a minor issue for most Internet users today, but it bears mentioning nonetheless.
Reason #12: Adobe Doesn't Even Use It
That's right! The very company that makes, markets, and distributes Flash doesn't have a Flash website! Perhaps because they know its limitations, but we'll let the irony of this fact speak for itself.
Needless to say, all The Zoo Group websites are non-Flash websites. Through our commitment to standards-based design, unrivaled SEO, and professional usability, The Zoo Group provides all of the presentational benefits of a comparable Flash website with none of the damaging drawbacks listed above.