Position is all, all is relative, position sometimes too

Position is key to poker, especially in holdem and draw where position is fixed throughout each hand.

Still position is not just being on the button or to the left of the villain that raised PF. Sometimes other things come into consideration.

But first, to explain why position is key, i will use an explanation for new players given by Mr Tannenbaum in one of the conferences he gave a couple years ago:

Poker is a game of betting. Throughout a hand, you bet that you will win the hand and your opponent takes the bet or raises it and viceversa. This is as simple as it gets...
You have a good hand and try to "sell" it to your opponent at the highest price getting him to bet more than he should when he is the underdog. OR you have a mediocre hand and try to get to showdown, or draw, at the cheapest rate considering your underdog status...

NOW CONSIDER THIS:
When you go buy a rug at a store and you see one you like and ask the owner of the shop, this middle eastern guy, how much the rug is, he responds by asking: "How much are you willing to pay for it?"
Why is he asking this? Why doesn't he just tell you the price? He isn't confused as to the price of the rug, he just wants you to go first saying a price!
He knows if he says a price right away, you are never gonna pay more than what he just said. You might pay that or you might pay less.
Whereas if you say a price...
1st it may be more than what he had in mind (he makes profit)
2nd he may respond with a higher price adapting his price to what you just said (he has some information to go on)

So, what he really is saying is he wants you to go first, he wants you to commit to an initial price FIRST. He will go from there. Getting you to go first will ensure that he gets the most he can from you.

But this explanation is an analogy to playing a pot heads up.
In raised multiway pots, another kind of position is also important, and this is where the whole "it's relative" comes into play.

RELATIVE POSITION vs ABSOLUTE POSITION

Absolute position is the button, is being last to act on all betting rounds, is important most of the time.
Relative position is your position relative to the most likely betting sequence in the next round of betting. It's also important and may be a whole lot different than being on the button.

Example hand:
You hold T9o in UTG+1
UTG raises

you should clearly fold this mediocre hand

Even if you could be sure that there will be more ppl in the pot (better odds for your marginal hand) and that no one will reraise behind you, this is still a fold.
When the flop comes, the PF aggressor will most likely throw in a bet and now you will need to act "first" before the rest of the other people in the pot.

Say the flop is not bad for you: J83 rainbow
You're still on a bad spot, since you don't know what the ppl behind you are gonna do. You may call hoping to draw to the OESD just to get raised and reraised by the ppl left to act. You may fold, fearing those possible raises, just to see everyone else fold too...

Now consider this same hand, but you are in the BB
again UTG raises
MP1 calls
CO calls
BN calls
SB calls

Now you can consider playing this hand.
Not only are you sure you will not get a raise behind you PF since you are closing the action, but on the flop, SB will most likely check, you can check, see how the betting goes, and wait till it gets back to you and "effectively" be last to act in the flop betting round.
Thus, on that same J83 flop, when the action gets back to you, you will know your exact odds, you will have information on the other ppls hands... You may draw to your straight if there are just a couple calls of the first bet, and you are getting good odds closing the action, or you may safely fold if someone raises and someone else reraises, indicating big hands and cutting your odds greatly.
See how the person on the button still has SB and BB to act behind him, so even though he has ABSOLUTE position, on the first betting round he doesn't have RELATIVE position.

YOUR DECISIONS ARE MUCH EASIER WITH POSITION (both ABSOLUTE position and RELATIVE position)