I took my laptop apart today

I have a laptop that has had a flaky screen for over a year. Finally today I had enough, and I took out the set of tiny screwdrivers. I ended up with 6 extra screws, one brass stand-off, and the defective microswitch, which had been causing all my problems, left over when I re-assembled it. Whenever I have had the pleasure of taking electronics apart I am struck by how many different sized screws are used in the design. While I understand different length screws I am not sure I understand why one would want screws of a different pitch or width. It seems to unnecesarily complicate assembly and repair.