Since most newer games are constantly loading data from the hard disk, you should see a benefit having games installed on an SSD, especially for games that have large map/texture files that need to be loaded each time you enter a new area. As UsandThem said, it probably won't be a HUGE difference, but it will be noticeable. Then put your static data that doesn't need to be loaded fast (music, movies, etc) on a larger, cheaper, slower drive since they won't benefit from an SSD at all.
One example that I like to use since my daughter keeps reminding me of it, is Roller Coaster Tycoon. My daughter loves that game, and on a WD Black mechanical drive it took about 5 minutes to go through the initial load process where the game puts everything into RAM. Installed on a Samsung EVO 850 it takes about 5-10 seconds to load. It doesn't make much difference after that since everything is in memory at that point, but it definitely gets the game started faster.