Threebetting for free showdown?

[RunDownHouse]

If I've got a fairly strong hand on the flop, like a pair + draw or sometimes TPTK, and I get c/r'ed on flop, I'll sometimes 3bet if I think I can get away without a cap and check behind on the turn. That way I get to showdown for 1.5 BBs, instead of 2BBs.

That's only an occasional play. Doing it on the turn is, as the other poster pointed out, "retarded," because you're paying the same, plus risking a cap when behind, plus risking a river donk. Best case: same cost for SD. Worst case: much more expensive.