There's allot more than just "streaming media" which needs to be blocked enterprise-wide (sure the marketing dept. is one exception)

But ESPN, NCAA, Netflix, Hulu, SyFy, TNT, CollegeHumor, etc. should also be blocked. I've also reclaimed bandwidth by blocking games, advertisements, forums, time-wasters like facebook/myspace, 3rd party (non-company) email and IM like hotmail/yahoo, Skype, file sharing/P2P clients, Tor and anon. proxy sites.

If your business doesn't use it, then there's no reason for it on your network.