Why block a bishop's check with another bishop?

I noticed in several chess openings that the preferred book line for blocking a bishop's check is to interpose with another bishop, rather than to interpose with one of the knights. Is this merely to avoid a "self-pin"? Or is there another idea behind it, like maybe "putting the question to the bishop" in a different way?

I'm also curious about the nature of such checking attacks. I've read that the Bogo-Indian Defense tends to be drawish because of this exchange, but does that mean that all such bishop-checking attacks tend to be drawish?

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(p. 221)
Self-Pin   In problem composition, voluntarily moving a piece into
an absolute pin. In ordinary play, it's usually an error--blocking a
check by putting your own piece in a pin instead of simply moving
the king off the line.

Pandolfini, Bruce. 1995. Chess Thinking. New York: Simon & Schuster.

There is no specific "rule".  Every opening is different.

After 1.e4 c5 2.Nf3 d6 3.Bb5, 3...Bd7 is simply safest.  It forces White to react to the threatened Bishop.  Interposing with the Knight is a line, though far riskier as it gives White time, you self-impede the development of your Bishop, etc.

Same reasoning for White in the Bogo-Indian.

1.e4 e6 2.d4 d5 3.Nd2 c5 4.Bb5+ (First off, too soon!  White should play 4.exd5 or 4.Ngf3.  However, besides that, is it not obvious that Black would be more than happy to trade off his Bad Bishop for White's good one?

There are no hard and fast rules in chess.  All rules have exceptions.  For example, White King on the 6th, White Pawn on the 5th, Black King on the 8th, all on the same file, is a Win for White no matter who is to move - WITH ONE EXCEPTION!!  If it's a Rook Pawn (i.e. WKa6, WPa5, BKa8 or WKh6, WPh5, BKh8), it's a DRAW!

You need to look at what each legal move does for you, and in some cases, which is the least evil.  Interposing a Bishop with a Bishop threatens to trade (or win the checking Bishop if it's unprotected).  Blocking with a Knight not only pins the Knight, but impedes the development of your other pieces in some cases.  You must watch out for this.  But again, there is no hard and fast rule that applies 100% of the time!

Thanks, ThrillerFan. That makes sense. It looks like I was trying to overgeneralize, especially with only a few examples.

I had forgotten about Black typically having a bad bishop in the French Defense, so trading off that bad bishop is definitely preferable for Black in that case.

I'm not sure the argument about impeding the bishop in the case of the Sicilian is logical, though, since ...Nc6 would allow Black's QB free reign on the open diagonal from c8 to g4.

I'll be watching for more openings with this pattern in the future. I suspect after I find a few more examples some general rules of thumb *could* be made, such as including if-then statements about good/bad bishops.

SilentKnighte5,

Nice counter-example, but "there ain't nothin' normal about them Budapesters."

P.S.--I just found another example, shown below. Since this is a QGD, an opening notorious for Black's problematic QB, it also makes sense here for Black to try to trade off that bishop by blocking the check with his bishop.

P.P.S.--And a counter-example...

P.P.P.S.--And another positive example...

The line I was referring  when saying that yu are impeding the Bishop wasn't the hybrid line (3...Nc6) that could also come via 2...Nc6 3.Bb5 d6.  I was referring to the riskier and possibly more dynamic 1.e4 c5 2.Nf3 d6 3.Bb5+ Nd7 intending 4...a6.