0The best time to trade men is when you can capture men worth more than the ones you will be giving up, which is called "winning material"But the opportunity to do this may not arise if your opponent is very careful.
Since you will probably have many chances to exchange men on an "even" basis, it's useful to know when you should or shouldn't do this. There are several important considerations.
As a general rule, if you have the initiative (your pieces are better developed, and you're controlling the game), try not to exchange men unless it increases your advantage in some clear way. The fewer men each player has, the weaker the attacking player's threats become, and the easier it is for the defending side to meet these threats.
Another time not to trade pieces is when your opponent has a cramped position with little space for the pieces to maneuver. It's tough to move a lot of pieces around in a cramped position, but easier to move just a few.
One sort of advantage you can often gain by trading pieces is a weakening of your opponent's pawn structure. If, for example, you can capture with a piece that your opponent can only recapture in a way that will give him doubled pawns it will often be to your advantage to make that trade.
The player who is ahead in material will usually benefit from trades. It's sort of like basketball or soccer; five players will sometimes have trouble scoring against four opposing players, but take away three from each side and the stronger team will find it easier to score with two players against one.
So, to summarize: It's usually good to trade pieces if your opponent has the initiative, if you have a cramped position, if you can weaken your opponent's pawn structure, or if you are ahead in material. There are exceptions, of course, but following these rules should bring you considerable success.
