Trading pieces

I've heard a lot of people say don't trade pieces unless it benefits you. I understand that I shouldn't trade if it benefits my opponent, but what's wrong about trading if it doesn't benefit any of us? I am very fond of trading, and like the games where there are few pieces left, usually if I manage to get to endgames with only pawns and a 1-2 pieces left each, I usually win. 

Fischer never had any pieces standing badly: he traded them.
The art is to trade your pieces that will stand badly for pieces of your opponent that stand well.
Also if you have an advantage, trade pieces, not pawns.
If you are behind, do not trade pieces, trade pawns.

I'll give you 2 pawns for that there rook.

Ignore the pieces that are coming off the board. Pay attention only to the pieces that remain on the board... THEY are the ones you will be working with.

Not entirely true. When up in Pawns, trade pieces. When down in Pawns, trade Pawns.

but if ur behind you might want to start an attack so you can trade or even sac pawns to open up files on his king

Against any sort of competent opponent, you cannot dictate where an attack will take place. The Pawn structure determines which part of the board you should be defending on, and where you should attack.

If your opponent has an advantage in controlled space, trading pieces will often bring a measure of relief. Three pieces rattling around in a cramped position are far less constricted than seven pieces stuffed into the same cramped position.