The Importance of Raising (versus Calling) in Poker
"If you plan on playing very tight and folding lots of hands, then a blind steal is necessary every once in awhile in order to stay alive. When raising, there is another important thing to remember: it takes a good hand to raise, but a good one to call as well...
"But remember that if there are antes, there is a lot more at stake and it's better to win the pot right there instead of seeing a flop."
-Dutch Boyd, dutchboyd.com
If you raise, you're often letting players know that you don't have a 7 2 offsuit (unless of course you're bluffing, but that still gives players the impression you have a good hand). If you raise, players will only call if they really like their hand. If someone else raises, you should only call/reraise if you really like your hand.
If someone raises 5x the big blind preflop, calling them with a jack deuce probably wouldn't be a smart call since they could easily be sitting on some paint. But when you have a stack, it is important to use it. If you can afford to lose a couple of your chips here and there, do it. If your stack is three times bigger than the player who is second in chips at your table, there's no reason to limp in with a hand.
If you let other players see flops for cheap, they might hit some of the weird cards they need for a straight or two pair, or even make a set. Simply calling is dangerous because it gives other players openings. How much you want to raise is up to you and depends on your strategy, but a raise is almost always best when you have a hand.
Your goal is not only to win the pot by showdown but push players out as well. Every chip counts and it's a lot better to be heads up with a player with a nice hand you can beat than playing against four players who all hold at least one picture card that they get to see a flop with for cheap.
Setting traps when you raise is also very helpful. Although it's difficult to do and you aren't often in the situation, it is great when executed. Let's say for example you have the nuts, or at least a hand you know you aren't folding and know you're probably winning with.
A player raises before it's your turn to act. Perfect. You reraise him, maybe 3x his bet, and depending on his chips he's probably forced to call. If this wasn't the final round of betting, then you really have him set up now. If he bets, you go all in.
If he checks, you bet as much as you can without making him fold. Either way you're money. Reraising is a great way to trap players and get them pot committed, winning you more chips by showdown.
Knowing When to Fold
Just like any other time in poker, sometimes you know you're beat and you just have to lay it down. If you raise with pocket jacks preflop and get called by one or two players, your hand is still good. But when the flop comes down and it's Ace King Queen suited, you have to really start thinking.
If someone bets big, you're probably beat. If anyone has an Ace, King, or Queen, you have to hit a jack (8% chance after the flop, assuming no one else is holding a Jack) to beat them. Or, they could have Jx suited or Tx suited and made their flush.
When there are three suited overcards on the board and you're looking at a big bet, you're probably beat and you have to just accept that and fold. Calling off more of your chips won't help you, so you just have to tell yourself you've lost some chips in a raise, you don't have this hand locked, and it's pointless to cripple your stack in order to justify your raise.
If you know you're beat and you know to fold without throwing more chips into a pot you've clearly already lost, you will feel a lot better when you watch another player call and get knocked out by the nuts or when you just think in retrospect that it could have been chaos if you called. Also, thinking that the other player is now a little aggravated because they didn't get a lot of chips for their hand should make you feel a little better.
So while raising is a great play, it's important to realize that raising does not automatically mean you need to call every bet the rest of the way.
Sometimes hands don't go your way, but at least when you raise you know that when that lame 2 5 7 rainbow flop comes down then you still have a nice hand since people most likely aren't calling your raise with low cards like that.