Originally Posted by
Missing_Minds
It depends on the case. Those are normally used to keep the mother board from the metal case (that board on the case will short everything out), provide a ground point, and... some of the earlier days were to help support the CPU. (these days the heat sink is designed to do this as well).
It also is used (now) to help keep the board from warping due to weight. (think of heavy books on a book shelf) With how multi layered some boards are, a little bend can end up being a very bad thing over time.
As a rule of thumb, I normally will always use them when holes are provided, and esp when there could be a bend possibility. Yeah, I'm paranoid.