The only problem with having Flash 8 is that compiling will be an issue if you have people using new version of Flash when you are doing collabs. But, the biggest advantage on using Flash 8 is that it is so smooth, fast, efficient, and basically all you need for animating. [ Brush sizes are a go, too. ]
Problems for the newer versions of Flash are that they require more CPU, RAM, they take up a lot of space, laggy as shit, you won't be able to partake in a lot of collabs, and crashes a lot. [ They even have unnecessary long-ass save times and such. ] Though the advantages are better features, more options, compiling advantages, and such. If you want to get the latest versions of Flash, I might as well suggest getting a stronger computer.