I have criticized myself in an earlier post of the same subject, and after the Winterthur Chess Week Open I must come back to this issue. Preferring Bishops over Knights, as Tempo does, is completely ok. What I call Bishop Fetishism is to make weak moves because of this preference. I did twice in my last tournament, and once it was the beginning of loss in the opening, and once it was a direct cause of loss in a late middlegame.
Let's assume for the moment that a single Bishop values more than a single Knight (it does not), then we speak of a maximum of 0.25 pawn units (half the bishop pair bonus of 0.5). In general, of course, as a mean value of 1 million positions. Making one passive move loses 0.25 pawn units, giving away the hypothetical maximum plus value of the Bishop. In reality, in most cases, you will be not equal after a passive move, but considerably down by at least 0.25. In many cases a weak move starts a chain reaction of more weak moves, and this is what you will end up with: A position where your Bishops have nothing to pin and where the opponent's Knights have wonderful perspectives to fork your weaknesses and to occupy outposts.
Here is my list of bad bishop moves:
- Developing on a passive square to prevent being attacked or traded away.
- Not recognizing that the Bishop will become a bad one and missing the opportunity to trade against a strong piece.
- Using too much time to maneuver the Bishop to its best square.
And these are the jobs I think a Bishop should do in a game:
- Pin or x-ray a target
- Work together with a Queen in a diagonal battery
- Work together in a Bishop Pair, controlling open space
- Eliminate dangerous or guarding Knights
- Destroy the castle of the opponent King
- Being a life insurance in an opposite coloured endgame with pawns down