ya sure..... but it is clubbed along with ur steam account, which means another steam account user wont b able 2 use/install dat backup. and make sure dat u use the inbuilt steam backup utility. dats the most safest mode of backing up steam data.
The way steam works is, even if you uninstall the game, or your HD dies, you install steam, and all the games you have purchased will show up in your Steam list, just waiting to be downloaded...no need to back up to disc.