Normal width men's snowboards are designed for men with "normal" size feet/boots--meaning about size 10.5 and smaller and sometimes about size 11--depending also on stance width, binding angle, and boot model.
Wide boards are for guys with bigger (than "normal") feet/boots.
The general belief is that you shouldn't use any wider a board than is necessary because an overly-wide board will be/feel slower when transitioning from one edge to the other (from edge-to-edge)--it'll feel sluggish compared to a narrower board.
However, I believe that some companies and people like a slightly wider than necessary board for freestyle(/"park")-focused riding because they think/believe/feel that a slightly wider board is slightly more stable than a slightly narrower board and I believe that this is why some freestyle(/"park")-focused boards are mid-wides.
Furthermore, when compared to all-mountain/freeride-y-type riding where you're frequently/constantly/continuously lifting your edges fairly high up off of the snow a-lot and rapidly transitioning back and forth from edge to edge a-lot--you want quick and efficient edging, but for freestyle(/"park")-focused-type riding where, most of the time, you're not really lifting your edges up as high up off of the snow and/or rapidly/frequently/constantly transitioning from edge-to-edge as often--this isn't as important.
I believe that:
normal width boards are ~254 mm and narrower,
mid-wides are ~255/256 mm to ~260-ish mm,
and wides are ~260-ish mm and wider.
ALSO, generally speaking, I think that it's safe to say that it's much better to use a slightly wider than necessary board versus to a slightly narrower than necessary board because it's much better to a have a slightly slower edge-to-edge transition than it is to have any heel and/or toe drag.
Last edited by PATKOUG; 11-16-2011 at 12:54 PM.