I can think of a few others, but the main downside is that wives don't like men to take naps, according to the always-wise Joe at Evang. Outpost:
We men realize that we are completely screwed up, yet, for some inexplicable reason, we don't feel the need to change. Since we can rarely muster the audacity to openly show disdain for the Master Plan, we have to take a more passive-aggressive approach. By napping we can enter an unconscious state where we don't have to think about our feelings, ponder where this relationship is going, or answer questions about why the floor around the toilet is always sticky.