Or it can be the difference of 5FPS in a game. Or the difference of a working processor and a burnpile. Or the difference between a broken computer and a working computer...
Not to scare you away from doing it or anything... I did it, lol. Everyone else did it!! (I jumped off that bridge. Landed on everyone else, and I was ok.)
But in all seriousness, it speeds up your computer, and its fairly safe, the computer will not operate correctly if you over do it, but it wont burn unless you WAYYYY overdo it.