Since in each round the Dealer, the Small Blind and the Big Blind are moved clockwise, every player takes the next betting position in the following round.
The player acting first is at a disadvantage to the player that comes last. This is obviously because a player in an early betting position doesn't know what the following players are going to do and if there are raises after a players action, the round may become more expansive for the player than initially planned.
On the other hand a player in a late betting position already knows what his opponents have done and can react accordingly, thus having much more control of the action.
Hence, the sooner the betting position, the stronger the hand must be. The later the betting position, the more information a player has gathered, before he has to decide whether to play a hand that is not particularly strong or not.
That's why the position is an important matter in Texas Hold'em Poker, not only in the Preflop but also in the betting rounds later on.
