When to trade pieces?


If you are wining trade pieces, if you are losing trade pawns, trade your passive pieces for actives ones, trade queens if you have less space, trade to deny counterplay and trade to ruin pawn structures (if it's worth enough).
The winning player trades pieces but not pawns while the losing player trades pawns instead of pieces. If trades are forced, the side with more material will win.

A piece for a piece does not always have to be the case. In the Italian, a common trade i see is trading off a knight and bishop for an attack on the castled king, a pawn and rook. While theoretically, this trade is equal, it is often not due to black being down a piece. Points do not equal pieces.

Sometimes the trade is made to then double up the opponents pawns. In the end, you must ask yourself if I make these trades am I in a better position to get an advantage. I disagree that just because you are ahead you should trade. If you don't see down the road the trade may lead to something like your opponent having a better chance at advancing a pawn storm.