Many Poker Holdem players consider checking to be a bit of a cop out. The general theory is that you should either bet or raise because a check signifies weakness.
Dont be passive
However, this can be a bit of a generalization. There are times when a check is perfectly justified, just as there are times when it really does signify a weak, passive player who is just waiting to be preyed upon.
If you continually check each round, following limping in pre-flop, then it will not be long before the other players get a read on your behavior and start to take advantage of your pattern. Your lack of aggression, by failing to bet or raise, will have your opponents turning up their aggression ratings to knock you out of each pot and your chip stack will disappear faster than a hotdog at an eating contest.
If a player who is normally aggressive suddenly checks, there could be several reasons for it. He could be holding the nuts and deliberately laying a trap, hoping someone will perceive his check as weakness and will bet into him. This tactic is known as slow playing or sand bagging. It occurs when a player is extremely strong, but acts weak to entice an opponent to try and bet him off the hand.
If you are holding a very strong hand, you may want to try a check occasionally to see if you can reel another player into your deceitful web and make some money. Of course, if you never raise and then suddenly push a bunch of chips in the middle, your opponent is going to smell a rat and get out of the way.
Taking your foot off the gas
Sometimes you dont know where you are in a hand and you need to check to see what is going on. You might have played aggressively up to the turn, but your opponent has called every street. Suddenly, your pair of kings no longer looks so great and you begin to think you might be beaten.
This could be a time to check, although bear in mind that if you are the first to act, your opponent is likely to bet after you. That is why acting last is so important. If your opponent acts first and checks, then you can check after him and take a free card.
Earning a free card
Sometimes, if you have been aggressive in a previous round, your opponent will check because he is worried that if he bets, then you will raise. Lets say you are holding the jack and ten of diamonds. The flop brings out two more diamonds and you bet. Your opponent calls and a club falls on the turn. You would like to see the river card for free. If your opponent checks because he is nervous of your aggression, you can check behind him and see the river for free.
A little aggression helps
Just bear in mind that checking on its own is very weak. If you continually check your opponents will smell blood in the water and circle in for the kill. Instead, combine the occasional check with your normal aggression and keep your opponents guessing.
After all, if they cant figure out what you are up to, then they will make a mistake which in turn makes you money.