I'll show in situations where it makes no difference: in BB, and everyone passes I show. They already forfeited their right to play.
After flopping something like quads, a big full, or straight-flush. Makes no difference as no one will be surprised that you bet such a hand.
Keep 'em guessing: raise it out of the #1 hole with (7,2-o), steal the blinds, then show. They won't be so sure the next time you pop out of an EP with a Premium. (Beware of those players who know what you're doing though that opens the possibility for pulling off a con/recon Level-3 play.) This works best if you take it down immediately. If you get called, float the flop, and steal it on the turn, it's TMI to show in that case unless you have some other, more compelling, purpose for showing.
It's good PR, shows you're a "sport", and it may keep them showing in situations where it makes a difference, like after making a hero fold, and the fish shows that he did, indeed, have the nuts. As with the straddle, if everyone's doing it, join in occasionally for good PR.
