At first glance, the raise would tell you that the person who raised has a winning hand. This would also tell the players with the not-so-good hands to leave the game to those who have the best hope to win the pot. By elimination, the raise would limit the player's chances to loose to a bad hand.
For players with experience, it is possible to use the raise to calculate what odds are there to win; however this takes some calculations and you need to be very well tuned into the poker game. This would be able to force your opponents out of the game when the odds would seem against them, or at least have them pay more to stay in the game that they had bargained previously.
A raise can also mean bluffing. This is something only veterans can do because the bluff can be very risky with inexperienced players. Bluffs raises are best when you know how the players react in certain situations and then you use it to eliminate them from the game. Bluffing is not for everyone because it can very easily be turned against the bluffer unless it is done timely and with proper calculation.
When in late position a raise could mean a ticket to get a free card or the opportunity to play a semi-bluff which would turn most often than not in a winning stance. In this case the raise is made before you have got your full hand to keep your opponents guessing about your real hand and intention. As mentioned earlier, the bluff is one of the best parts of the Poker game. The raise when used for a bluff can become a powerful tool in your favor for winning the pot.
1. Bluffing to force your opponents out is done with finesse and requires a lot of experience to pull it off correctly. If it is not done well and your bluff is called you would end loosing not only the game but also a lot of money.
2. When you are just about to win, you need the raise to keep other players in line until you get the card you need. This would buy you time and increase your chances to win.