As with anything else in life, there are pros and there are cons. As the master user, you are the one to decide if the con outweighs the pro or vice versa. Of course you always have a choice when doing a website, static, dynamic, flash, etc. But you also have to look at the pros and cons not just from an owner view, but from a user view. Flash based sites have been a hugely popular thing to add to your site over the last few years, Macro-media has constant additions and features being added to flash so we can only predict that more and more people will use them. However, flash sites often have said to be unnecessary and overloaded. Here is a breakdown for you, and then you can decide if you really want to go Flash Based or not:
Interactivity – Flash's Actionscript opens a vast amount of possible actions. Software Engineers, and designers have utilized Flash to create interactive characteristics arraying from very lively feedback forms to appealing Flash-based games. This absolutely new degree of interactivity will always leave people coming back for more!
Standard Site – With flash based sites you need not worry about browser compatibility. No more woes over how a particular css code shows differently in IE, FF and Opera. When you position your website elements in Flash, they will always appear as they are, as long as the user has Flash Player set up.
Better Expression Through Animation – In Flash, you can make use of its animating benefits to convey a message you're trying to make in a much more efficient and effective way. Flash is a light alternative for animation because it is transmitter based (and hence smaller file sizes) as opposed to real "movie files" that are faster based and hence much greater in size.
The Bad & The Ugly:
The Player – People absolutely will have to already downloaded the player beforehand or they will not be able to view flash movies. I know the annoyance is not lost on just me, I know a lot of us have gone to a site that only allows flash, and it will not allow you to see anything unless you have the newest player on your computer. Frustrating. And even more frustrating in most cases you can not just download the player and be on your way, no, you have to reboot, restart your browser, go back to the initial site and try again! It takes too much time, and you can in turn lose customers by having flash on your site.
Optimization – In most cases, if your website is in flashed based form, search engines will not be able to index your content. Which in turn means you probably will not rank well in the search engines and that means you probably will not be getting as much traffic as you would have, if you had a regular website, with no flash!
Loading Time – You want to get your customers / clients / users attention ASAP, the last thing you want to do, is losing a potential customer because the text and or image took too long to load. The longer it takes to load, the bigger risk your chasing that your customers will not stay.
The best way to go is to use Flash only when you absolutely need the interaction and motion that comes with it. Otherwise, use a mixture of Flash and HTML or use pure text if your site is purely to present simple textual and graphical information.