Originally Posted by
MickR
The idea is to reduce the beard on each pass. With a straight razor you have a single blade doing one pass with lather, then a second after re-lathering and so on. With a mach 3 you have three blades covering the same ground. The first takes some hair and the lather away, then number two and three blades come along running on bare skin to take away a bit more each, which is why a modern blade is more prone to give you irritation and ingrown hairs, and also makes for a smoother WTG.
Mick