It provides you with a snapshot of your system including programs, license keys, system profiles, etc. It's a handy tool to keep track of all of the stuff on your computer.
WinDirStat is another good freebie. Gives you a treemap view of everything installed on your computer (programs, music, movies, games, etc). If you want to know what stuff is taking up the most space this is a great program to see it visually. Looks like this after you run it: