Well there's obviously no blanket answer, it just depends on the individual body of water. Hell I know of a cove here in LO where crappie can be caught in 2-3fow all Winter, no spring influence, no massive amount of cover, nothing special that you'd ever recognize....but for some reason they are there. Next cove over...same water temp, same N-S-E-W orientation, same bottom composition....but no crappie. Crazy! It's like trying to figure out why your wife sits with her legs crossed, and your girlfriend sits with both feet in the floor.
Ooops! Did I say that outloud?