Bishops and pawn chains

OK, I didn't really know which forum to post in, sorry if this is the wrong one.

My question is a sort of genral one, in e4-e5 openings, when Black plays Bc5 followed by d6, the bishop is kinda trapped on one side of the pawn chain.

Is it worth going ater a Knight for Bishop exchange with Nc3-a4? Should Black first have created an escape square on a7 with a6?

eg:

bishops are generally more powerful than knights, especially in the endgame, save for the obvious forks and if a piece is blocking the bishop, so I would say yes play na4

Probably not such a good idea at this point as you would be leaving your e4 pawn unguarded.

Ok, point taken, lol. I was actually asking about such positions in general.

Eg, in the 4 Knights, the White Bishop often ends up in the same sort of position too.

I am not very familiar with this issue in the context of a king's pawn game, but more so in the context of a queen's pawn game (think colle or slav defense type structures). Obviously in that case the issue is about Bf5 vs. a subsequent Nf3-h4 instead.

I haven't come to any clear-cut conclusions about this (sorry). I like bishops and so when I lock my bishop out of the pawn-chain and the white player comes in and forces the exchange with a Nc3-a4 or Nf3-h4, I am unhappy.

If I feel I can afford the time (maybe my opponent is lower rated or poor at opening play) I play a6 or h6 to prepare the development of my bishop by providing it with an escape square. However, I feel that this is kind of a lazy and ineffective adjustment on my part.

From the white perspective, I think it's considered sub-optimal because you are spending time to go and get that bishop - white has other priorities. Black gets compensation for the bishop pair in the form of an open a-file (after 1. d3 Nc6 2. Na4 Bb6 3. Nxb6 axb6 from the diagram). However, it might be a psychologically effective play because this might not be what black is really hoping to get out of his position - doubled pawns, etc.

I think that the exchange is acceptable for both white and black. I personally feel that you should be more concerned with other lines, though. How about:

1. d3 Nc6 2. Bg5 or

1. d3 Nc6 2. h3 (2. 0-0 Bg4 is annoying)

And other more principled approaches to the position.

I realise my post kind of sucks but I am just trying to be helpful.

edit: to clarify, all move sequences begin from the diagram

Thanx, essnov.

Acceptable for both is sort of the way I feel too. It's just with White I really dislike a bishop eyeing my f2, (subjective, I know), But the downside is you have to deal with a Knight outpost on c5, or an open a file for Black's Rook....

It is an interesting question and I've asked it myself. The advantages seem to be gaining the bishop pair and doubling pawns although if the bishop retreats to b6 first then you are also opening a file for the a8 rook and moving the rook pawn (generally considered the weakest pawn in end games) to the b file so I guess it's a bit of a trade off of advantages really.