Back in the 2000’s, When Flash came out first time with its smooth animations and sound support, It amazed me. I learnt Flash animations so that I can make my website cooler (I know but It was early 2k) but now days I recommend my clients to tick off the flash off their project list for following reasons
Stability and performance issues
Flash can make low end machines crippling slow because it guzzles resources like nothing else. Remember the browser crashes when you tried loading it in the past? Yeah.
Who would like to encounter a 3-minute intro before browsing the website? Newsflash: No one has that much time. It also uses some effects (Mouse Roll over) that touch devices can’t understand, and try navigating a website with flash navigation, It’s the easiest recipe to hate your life, and don’t even get me started on that horrid UI/UX.
Developer use different JS libraries (JQuery, the most popular) to have great visual effects and animations on your website without straining your system. You can embed a video with HTML5 without any Flash these days. How cool is that?
Apple don’t and wont support it.
Apple devices don’t support flash. You won’t like to sacrifice a huge chunk of visitors to have some funky animations on your website. Would you?
Its disaster for SEO
Its internet age and Everything comes down to the SEO aka Search Engine Optimization. Search engines don’t recognize it. Simple. Search Engines loves to parse content. While flash can provide them some meta tags but It really effect the search engine optimization of your website in negative way.