This might be done, for example, when the first player believes that an opponent has an inferior hand and will not call a direct bet, but that he may attempt to bluff, allowing the first player to win more money than he would by betting straightforwardly. The key point is that if no one else is keen to bet, then the most a player can raise (in a limit game) by is one single bet. If someone else bets first, he can raise, therefore increasing the value of the pot by two bets. In a no-limit game, there is no restriction to the size of one's bet and a raise is likely to be much larger than the second player's bet. Of course, if no other player chooses to open, the betting will be checked around and the play will fail.
While it can be an important part of one's poker strategy, this play is not allowed by a house rule in some home games and certain small-stakes casino games. It is also frequently not allowed in the game of California lowball.
Check-raises can also be used as an intimidation technique over the course of a game; a player who has frequently been check-raised may be less likely to attempt to steal the pot.
Not all players agree that a check-raise is an especially effective play, however. In Super/System, poker legend Doyle Brunson claims to check-raise very rarely in no-limit hold 'em; he contends that it is more profitable to simply bet a quality hand, regardless of whether his opponent will try to bluff. His reasoning for this is twofold: Firstly, a failed check-raise gives other players the chance to see free cards that may improve their hand, and secondly, it makes it obvious to other players that you potentially have a very strong hand. The latter, however, may be used as a strong bluff technique, although the opponent could put in a reraise to scare off a bluff.