[DarkMagus]

You make a small raise so that it's easier to stack someone when you flop a set and they have something. Think about the bet sizes you have to make.

4 people to a limped pot:

Flop: .40 in the pot. You flop a set, bet .40, get a caller.
Turn: 1.20 in the pot. you bet 1.20, and he calls.
River: 3.60 in the pot on the river. you bet 3.60 and he calls.

You have to make huge pot bets on every street, and you still only won $5 - half his stack. If you're lucky enough, he may have a good enough hand to raise, but this won't happen as often.

Now let's look at the same situation in a raised pot.

Flop: 1.60 in the pot. You flop a set, and bet 1.2 and get a call.
Turn: 4 in the pot. You bet 3 and he calls.
River: 11 in the pot. you Shove for 5.4 and he calls.

In the raised pot, you managed to stack somebody, and you only had to make 3/4 bets instead of pot bets, which probably gets your opponents to call with a wider range.

Another advantage to the raised pot is that if your opponent raises you even once post-flop, his raise is probably so big that he's committed to calling a push. In the limped pot, he can easily fold to a flop 3-bet.

Disadvantages of this are that you have to pay more to see a flop you'll often be missing, and you open yourself up to a preflop 3-bet which you'll likely have to fold to, losing some money. However, at this level, the other players rarely 3-bet, and play bad enough postflop that these disadvantages do not even come close to outwieghing the advantages of raising.