When you know what hand a person playing against you has, this can give you a big advantage in various situations. It's not only about betting, it's a lot about reading what your opponent has by their reactions, body language, and betting. Some people have a certain style of betting you can get used to, the best poker players are the ones that variate their styles of play.
Betting style is also very important. Personally, I love to trap people, this means if I have a fullhouse on the flop, I check and wait for someone to try and bluff, or better yet I would go all in right away of it was a big pot. That way, they would expect me to be bluffing and would therefore call me.
There are so many different tactics and styles in Texas hold em, especially in no-limit texas hold em where the betting is open. That's where you really need to be very clever and try to bluff yor way out of a bad hand for a very good pot.
It's a great game.