is it bad to exchange a bishop for a knight?

I know a friend, his rating is in 1600s he always plays the 4 knights opening, and always exchanges his bishop for a knight, and he sometimes win against players rated in 1800s.

I like to keep my bishops, and i know that a bishop is more important than a knight in the earlier stage at least, bobby says that a knight is 3 pts, a bishop is 3.5 pts.

I wonder if anyone around here likes to exchange his bishop for a knight, and if you do so, how you play the game?

I would want bishops to where I can use them most which would be open positions, most commonly in the endgame. I would favor knights in the beginning and middle because there are still allot of pieces on the board and its a closed game because knights can jump over pieces.

Play like Fischer

so would you attack my knight with your bishop in the 4 knights game? Would you exchange your bishop for my kight? or would you play a less aggressive game?

Yes, it is very bad. Bishop is stronger than a knight.

I wouldn't take the exchange, but not because it is unplayable.

There are books on sacrifice variations.  It is best to attach no value to the pieces on the board.  At advanced levels a player knows how to confound opponents by sacrificing pieces against their value.  By understanding positional play and long term strategy it is clear that there is no definite answer to this question.

@pellik that's what happened to me, i played against my friend twice, the first time, he traded his bishop, and he dominated the center of the board with his knights, i had a bad black bishop for the rest of the game, and i couldn't move my pieces to castle on the queen side, so i had to castle on the king side, he was dominating that side, so i knew i was going to lose, but i had to castle, and eventually lost.

Now I'm playing a remach, he also traded his bishop, and now my king side is a mess, he can just keep attacking me and i will eventually lose lol

Here's the current match, i have an open file, which is good, but im gonna lose anyway lol :) (that's called optimism)

http://www.chess.com/echess/game?id=66532632

and that's the game that i lost :) (i shouldve won the game, but hey i've been playing for 2 yrs or less, he's been playing for decates)

http://www.chess.com/echess/game?id=65437026

Bobby Fischers point of view: Knight - 3 points, bishop - 3.25 points

It's also worth noting that Boris Spassky wasn't from FRAnce. 

I tend to favor bishops over knights, especially the bishop pair.

The biggest advantage is in case of an endgame with unequal numbers of pawns on both sides of the board (left and right) in which case the speed of the bishop to switch from one side to the other, or to control both sides simultanuously, is often deciding.

I had endgames, where it was exactly this kind of position, and my knight was stronger than the opposite bishop. It just so much depends on the actual position.

I remember reading some statistical study of GM Kaufmann according to which the advantadge of bishop vs knight is on the average due only to the bishop pair, worth half a pawn according to him.

But of course, the actual position is a much more important factor than the slight difference on a 10000-game average.

I took the game from Chess.com game explorer, so shame on the bad archive as always...