@1
"positional advantages are less clear and often less permanent than material advantages"
++ Not necessarily. A weak pawn is a positional disadvantage that is just as permanent as a pawn down. It often results in a pawn down in many moves. Positional advantages are also clear to identify. Converting them however is no easy task.
In chess books we often find evaluations along the lines of 'White is clearly better' or 'Black is somewhat better', although the position is materially level. There are positional advantages which cause us to give preference to one side or the other. However, we must admit that positional advantages are less clear and often less permanent than material advantages. It still requires good play to turn these advantages into either a mating attack or a win based on material. Despite that, in the hands of an experienced player these advantages are of serious importance.
We have already studied various positional elements. The control of the only open file can represent a great advantage. An inferior pawn structure or some weak squares can cause us a headache. The good or the bad bishop, the activity of the pieces, the mobility of the pawns, good or bad coordination of the pieces; these are all important factors in the position.
A positional advantage can be the result of the opponent's clumsy play, or it may be provoked by pressure being put on his position. Sometimes such an advantage is the result of one or more exchanges - if, for example, we exchange off our opponent's 'good' bishop, he might end up being left with a 'bad' bishop.