Studying chess: Questions

In studying chess I come up with alot of questions (see "to play or not to play")such as why is it in a exchange it is sought after to eliminate your opponets pieces but by therefor eliminating yours to to be up bye a pawn in the end game. And while this is a winning stratigy, it seems to me that in doing that your wasting alot of material when it could be put to better uses to get a faster mate.

Another thing that bothers me is why is it that the majority of games devolve into both sides with the queen and two rooks, in looking at games its almost seems that the knights and bishops are thier to just be taken in exchange.

Right now I am studying Understanding Chess Tatics by Martin Weteschnik, and while its a great book on tatics it seems that alot of the games that he sites have moves in them that are totally incoprahensible (Morphy-Anderssen Paris 1858 move 26. Kxb5 axb5).

Now the question is is thier not a better use for Knights and bishops than to just trade them off or just waste them?