Plywood and drywall are designed to bear loads per certain criteria.
Part of that criteria is span per framing member. Code also specifies span.
24" is acceptable for ceilings and roofs where there is USUALLY no more load than it's own weight. Floors and walls are exposed to traffic daily and require shorter span distances. Drywall on 24" centers will flex enough to crack at the joints when a person leans against it. Floors will sag and begin to crack when exposed to traffic on 24" centers. Say you have a warped stud in the wall. 24" centers will magnify it much more than 16" centers because of the lack of integrity and unity in the construction. Every stud helps the next just like the spokes in a bicycle wheel.
Zen, Ying and Yang,, Mang