Why you shouldn't limp:
I think limping is pretty much always bad, it doesn't accomplish anything is a good way to lose money over the long run.
For the most part people who want to play poker well should be playing a tight range. Depending on the table size you are selecting this range can vary, and if you are playing in a tournament this will be more variable. However, we should mostly be playing a tight range. Strong
hands and position are the tools that we have at our disposal, so lets use them.
If we are playing a tight range then we need to get value from the hands that we decide to play. The best way to get value from your strong hands is to put money into the pot. The best way to get money into the pot is to bet. The more you bet the more money is in the pot. Not only that but it makes people fold, if people fold we win without a contest - but maybe I will get into that a little bit more later.
I saw someone write that they will limp with AA because they want to build a pot by letting other people limp in. Reconsider your thinking on this. Lets say you are UTG and you have AA, you don't know how many people are going to enter the pot with a limp. Based on your strategy you are hopeful that 4-5 people will call you. so lets say its $1 blinds, just for simplicity sake. This means that you will be playing a $6.50 pot against 5 opponents. Your
equity in winning that pot is ~60%, or $3.90, another way to look at it is that you will win all of that $6.50 60% of the time, either way is fine, but lets just call it $3.90. That's profitable, though if we were to expand that analysis you are likely to put more money into the pot and if more money goes in then the
odds of winning a big pot change.... but for now we will stop at the flop.
So if you bet, lets say you want to raise it to 3bb, or $3. You get 1 caller for $3 plus the bb and the sb. You now have a pot of $7.50 against 1 opponent, our equity there is around 89% or ~$6.68.
So by betting 1 time with 1 caller we not only have a bigger pot, but we also have more equity because we are against fewer players with a stronger hand. The difference in equity there is a difference of 2.8bb's. That means when you limp to "get a big pot" you are actually giving up on almost 3bb's worth of value. So limping there lost us money. So playing a tight game we should be more profitable betting than we are limping. So while limping there is not "bad" as it will still make us some money it is WORSE than betting.
Another reason that limping is bad is when you take that same idea and use a hand with worse value- or one that should lose most of the time. If you limp with a low equity hand you are going to more often lose than win. I wouldn't be surprised to see someone losing a little less than .5bb's with weak holdings when they limp. Part of the problem is it takes a great deal of skill and experience to be able to play in a multi-way pot, especially if you are out of position. You have to have a very good understanding of that your opponents holdings could be (which is hard if everyone limps) and you have to know you are holding a monster if the stacks move into the pot.
The other reason to bet is that if others are limping and we are in position then we should bet to take their bb's. If we have a strong holding and are in position we should expect that not everyone will call your raise, which is instantly profitable when everyone folds. If you reduce to 1 opponent then you have built a big pot with stronger holdings in position. This is just pure equity. I love to play against people who limp call. Even if they play back at me on the flop I still make money off them because my hands are better than theirs most of the time.
So there are a number of reasons not to limp, part of it being that limping is worse than raising even if it is not strictly a losing play.