I always tell developing players that if they want to be good, they must learn to play tight. But, if they want to be great, they must learn to play loose. Let's look at both styles and see why this is true.
In cash games, especially those with full tables, one of the most important attributes of the winning player is the ability to wait patiently for quality hands. You might try to wait for good shorthanded games, but if a game is really good, it always fills up. When someone is "giving his money away," seats fill up with amazing rapidity. The facts that you have just lost a big hand and are bored or tired are no excuse; you must be capable of tight play to win. Even in tournaments, there are times (usually at the beginning) when the blinds are small and the chip stacks are big. Don't be in a rush to play hands during these periods; just be tight and patient.
Why should you learn to play loose if you can be a consistent winner by playing tight? Being a successful loose player is much harder than being a successful tight player. You are playing a lot of marginal hands, and thus your poker skills must be a lot stronger. You must squeeze every drop of profit out of your winners, while holding the losses on your frequent losing hands to a minimum. This means that you must read your opponents very well. It means that you must learn to use tools like slow-playing and value-betting at the proper times. It is difficult, it is tiring, and it can be very frustrating when marginal edges don't come through, but it is a great way to develop your poker skills. Players like Daniel Negreanu, Phil Ivey, Gus Hansen, and David Benyamine are tremendous loose players. This doesn't mean they can't be tight when the situation calls for it, but it does mean they have the skills to maximize their results with hands that Chip Reese, David Grey, and I probably wouldn't consider playing.
Another reason for learning to play loose is what Doyle Brunson refers to as "shifting gears." When everyone sees you as a tight, solid player, you can start to steal a lot more pots. But at some point, the table will realize this and start to give you more action. When this is the situation, you need to have the ability to play loose and still show a profit.
A hidden benefit of this loose style is the extra action you get with good hands. Look at it from your opponents' point of view. They see that you are playing a lot more hands than a tight player would, so they must give you a lot more action. This means that you will make more money on your good hands. You can't, however, give back this additional profit on the more questionable hands. Someone once referred to these hands as "high variance, low expectation." This means that playing these hands will exaggerate your swings (bigger wins and bigger losses) without adding much to your profits. The gain comes when you pick up a hand with a high positive expectation and win more because your opponents have seen some of the marginal hands you play.
If you play in an area where there are private games or home games, you will be much more popular and receive more invitations to play if you are an "action" player than if you are a "rock." Even though a great action player will win much more than a rock, he appears much more desirable for a game. This is true even in a casino environment. When a new game is starting up, players will join someone who gambles and avoid someone who waits forever for a good hand.
Today's tournaments reward loose play. There are periods when the antes and blinds are huge compared to your chip stack. You must play a lot of hands, and you must play them well, in order to survive. Top tournament players like Mike Mizrachi, Alan Goehring, and John Phan are capable of accumulating mountains of chips when playing garbage hands. On their good days, their bluffs work, their weak hands hit, and their strong hands get paid off. On their bad days, they make an early exit and have enough time to play golf, see a movie, and rest up for the next day's event.
I hope that I have convinced you of the importance of learning to play loose as well as tight. But how do you learn this important skill? Some of it can't be taught. It is a natural instinct, or what is often called "table feel." But like all skills, it can be developed. Practice helps. Sign up for a small tournament or play in a game that is about 25 percent of the stakes you normally play for. Make it a point to play a lot of hands. Bluff. Raise in situations in which you might normally call. Call in spots where you would normally fold. Later, reflect on this session. Try to see where you could have won an extra bet or avoided losing one. Notice how the table perceives you and how you can take advantage of it. When you return to your regular game, you will have added a few new moves to your repertoire. 