There's nothing terribly wrong with raising a small PP from LP after three limpers if you're confident they'll just call. You're getting close to your odds of hitting a set (1:5), and you might have the option of taking a free card if you're last to act. You can also represent an A if one flops or an overpair.

What I don't like about it is that a smart EP opponent will use your tendencies to raise from LP against you by limp-reraising, and you'll have to fold.