Nf5 Bxf5, exf5.
Positive Side for Black is the doubled 'f' pawns but the negative side its more valuable bishop has been exchanged with less valuable knight.
How can white decide, whether it is to be played or not?
Nf5 is Good or Bad
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Sep 15, 2017
0
#3
From a glance, it seems like a strong move. Black has the bishop pair. So if black wishes to double your pawns, he will have to give up this advantage.
My gut instinct is to take. The Knight on f5 is stronger than both Black Bishops, and unless Black play the undeveloping Bf8, he can't keep the two Bishop advantage anyway.
It should be noted that White only has one Bishop, so Black trading Bishop for Knight isn't really losing the two Bishops, especially if we back up a few moves. It's likely that White had played Bb5 and then Bxc6, perhaps as a Ruy Lopez Steinitz defence or something similar. Now, a few moves after, he plays Nf5. This is an extended series of moves where, in essence, both Bishops and Knights are being traded for each other. Thinking "Muh two bishops!!!!" isn't very useful when viewed in this context.
Anyway, Bxf5, then you can castle and play d5 and you have a nice central pawn and an open diagonal for your remaining Bishop. Seems reasonable enough. If I'm White, I likely delay Nf5, as I have more space. Something like h3, keeping the Bishop out of g4 and keeping Black cramped. Then Re1, Be3/g5, bring Rooks to center, maybe try for an e5 push.
Sep 15, 2017
0
#5
Nf5 is fine in similar positions... but I wouldn't consider it during the opening. Whether you're aiming for a pawn storm or piece play, in a position when:
1. Your development isn't finished and
2. Black has good central control and
3. Black isn't even castled yet
All make the idea look premature.
Sep 15, 2017
0
#6
pfren wrote:
Why should it be a good move? It moves a piece for the third time only to be exchanged, and after exf5 white's main trump (better central control) goes south.
The best move may well be the odd-looking 9.Qf3, which has the positional threat of e4-e5 followed by Nxc6, when white will eliminate Black's bishop pair, while keeping the more intact pawn structure.
The point is to get rid of black's bishop pair which can prove quite annoying. SO I consider it a decent move.
Sep 15, 2017
0
#7
LeonSKennedy992 wrote:
pfren wrote:
Why should it be a good move? It moves a piece for the third time only to be exchanged, and after exf5 white's main trump (better central control) goes south.
The best move may well be the odd-looking 9.Qf3, which has the positional threat of e4-e5 followed by Nxc6, when white will eliminate Black's bishop pair, while keeping the more intact pawn structure.
The point is to get rid of black's bishop pair which can prove quite annoying. SO I consider it a decent move.
There are competing platitudes 
For example when your opponent has less space you should not seek exchanges.
Qf3 with the idea of Nf5 comes to mind.
Positive Side for Black is the doubled 'f' pawns but the negative side its more valuable bishop has been exchanged with less valuable knight.
How can white decide, whether it is to be played or not?