Yes, technically speaking, you can do some pretty neat stuff with Flash, but there are three major drawbacks: they’re difficult to manage, they can potentially destroy your search engine optimization, and they can be incompatible on some mobile devices.

Let’s start with management. Flash just isn’t as portable and flexible as other methods of coding. From a programming perspective, integrating a full-flash website with a user-friendly content management system can be challenging and arduous (aka expensive). Major changes to your design, depending on its complexity, could cost you a pretty penny, not to mention the inconvenience. Simply put, it just isn’t as practical to build a site in Flash, especially if the client wants to manage it on their own.

Then there’s the search engine problem. This is probably the most dangerous drawback to a full-flash site. Unlike  HTML or other methods of coding, Flash doesn’t render text or coding in a way that is easily accessible by search engines. Because of this, search engines can’t pull information from your site necessary to rank it. You might as well not have a website if you’re hoping to get traffic from search engines.

The final drawback is compatibility. In order to view Flash in your browser, you must have Flash installed. It is pretty standard these days, but there’s still the off chance your visitor doesn’t have it, or is running a very old version. More importantly, some mobile devices don’t even support flash. This could have a negative impact on your business if visitors find issue with your site.

So, pretty much what I’m saying is don’t get too excited about Flash. That’s really all that it is. Something flashy to be used in moderation. There are better, more efficient ways to create a dynamic site, like using jQuery, which will keep your site easy to maintain and search engine optimized. There are many examples of jQuery on this site, which include scrolling elements, tooltips, overlays, and galleries.

In the end, if you mention to your designer that you want a Flash website and (s)he raises no concern, you may want to reconsider whether they have your best interests in mind.