This puts more money in the early pot and encourages players to fold early weak hands that could get a lucky flop and beat you.
If a 9 8 7 flops, you want to be playing the J 10 and not the 6 5 or the 10 6.
This includes suited cards that can't flop a straight. Both ends of a straight such as 9 5 fall into this very weak category.
When dealt 66 down to 22, don't play the hand from an early seat and from the late positions, but only when the price is right. If you don't flop a set (trips or fours) you should usually fold.
If you can make a straight AND a flush or trips etc., usually bet/raise your hand.
(= a three suit "rainbow" with unconnected medium and low cards). Usually fold if someone raises.
They can easily turn into straights that can overtake your high pair or other good hand.
Players that are close to all-in often rush the betting just to get all their chips in a sink-or-swim last hand.
In this case, you should usually hold the nut in that suit, or have trips or two pair that can fill up.
It is a way to vary your play and not be too predictable. You win pots that you don't deserve when your bluff works. You lose a few chips when it doesn't work but it will get you calls from weaker hands down the line when you have a strong hand and need the action.
. . . Especially when you are not playing hands and can pay careful attention! Do they find more hands to play than they fold? Do they bluff? Can they be bluffed? Do they have any "tells" (give away mannerisms) that disclose information about their hands etc.