I realize that its 2013 and the flash media debate is pretty much a peripheral debate at this point. Being in the web design industry, it is still a common occurrence to be presented with a job or project that requires migrating a corporate website away from the dependance of static flash media.
There’s a few things to consider when thinking about the negative impact flash can have on your site, all of which I would consider to be equally relevant :
In the last 10-15 years, the number of different devices that have connected to the internet has grown exponentially. One of the largest directions the mobile device and mobile operating system development has taken is to strip out any support for flash media on the mobile platform in general.
This can be typically justified by the additional processing power that is required to render and interact with Flash media. With mobile devices scraping every last drop of battery power to competitively offer the longest battery life possible, it was a no brainier to strip out support for flash media.
As a result, many websites with flash media will not render properly or at all on mobile and tablet devices. Your cutting out a large portion of potential traffic if you are a heavy flash website.
Search Engine Optimization
Google cannot pry into a compiled flash binary to determine the content and index it as such. This is a huge loss to websites that want their products , company announcements or any other content to be indexed by google to help drive more traffic to their sites.
As a result, even linking to specific pages or sub pages within a flash binary is practically impossible. You might as well cutting out the liklihood of sharing on social media as well.
Closing your entire site to a compiled binary is just not the way things have been going with the internet. Keeping your site open, easily indexed and easy to navigate will not only keep your end-users happy, but will keep all the indexing services like Google and Bing very happy with your site!