Answer #1: Information.
The later we are to act in a hand, the more information we have about what our opponents at the table are going to do. Said simply, if they have to act first, they have to give away information about both their hand strength and their line intentions before we do. Getting to act last means we can decide what to do with our hand based on information about their hand and line.
Here's a really simple but important example of this concept in action. We are dealt a pair of sevens UTG in a full-ring game. Sevens look strong, but with eight people yet to act, we're entering the pot basically blind. Now, I'm not saying we should or shouldn't open the sevens here (it depends on a lot of other factors), but we're putting money into the pot without knowing where anyone else is in the hand yet. In this particular case, we end up shoveling in more dough than we should when we call the first re-raise... and then we still don't even get to see a flop.
All-in for now...
And if you can't see the video due to mobile device compatibility issues:
|Hand History converter courtesy of pokerhandreplays.com|
|Seat1:||seat 1||($200)||Small Blind|
|Seat2:||seat 2||($200)||Big Blind|
|Dealt to hero|
Flop (Pot: $307)
Turn (Pot: $307)
River (Pot: $307)
|villain #1 SHOWS|
|villain #2 SHOWS|
|villain #2||wins the pot: $307|