[x] Limp/calling is fishy and you have ZERO initiative postflop
[x] Limp/calling and suddenly coming alive turns your set faceup vs anyone that's paying attention
[x] You're prone to a better set
[x] By limping you're inviting other marginal hands in on the cheap - small pairs do not play well multi-way
[x] It's harder to get creative/paid off when we do hit since we're OOP
I could go on...