Yes, it will clean uip some room. Just remember that when you delete stuff, you also need to go into your "Recycle Bin", and delete the stuff in there. Because if you delete something, it still stays on your harddrive until you delete it from your recycle bin.
Picture it this way. Take a box full of photo albums out of the attic. Start taking the albums out of the box. It gets emptier, right? Same with a HDD.
Yet even if you do all this, you can still get it all back. I dont think there is ever a way to get rid of things.. the FBI an such can always get it back. Hell, when my cousin bought a used comp from some pon shop thing, the guy before "deleted" everything off his HDD, my cousin can get it back, and there ended up being tons of child porn on it.