"Don't go broke in an unraised pot" - just rabbiting what previous people have said really. A hand like TPTK plays well vs one or maybe two villains, especially in a raised pot where underpairs, draws and weaker kickers may abound. In an unraised pot, there are likely to be several limpers, including the blinds who could literally have anything. So it becomes impossible to put the villains on hands, but you still need to bet to protect your own, and the next thing you know is you're calling a turn raise, the villain leads the river, the pot is bloated and you've still only got TPGK, and you get near-stacked by the big blind who holds J4 and pwns you with a two pair hand he'd never have had the chance to make in a raised pot.