One of the first things I learned at poker was the positions, and for some there is lot of material to read about it, so, yes, its a huge impact at my play.
Knowing what your opponent will do before your play will always be to your advantage.
Things like this are topics that deserve a lot more than a couple of lines in a post. Poker Mike made a great suggestion above about CCs poker course (free) and I can only underline that.
Of course, the position of the player at the table is a fundamental factor that must be taken into account when making decisions. Otherwise, it just doesn't make sense to play poker.