user20677: Assuming one or both players makes a mistake and transposes a bishop and the adjacent knight when setting up the board, would this help or hinder them?
The answers to this similar question suggest it's a disadvantage. However using the lichess board editor for different variations of this (one vs both sides with both on light squared or dark squares, etc) generally shows a larger starting advantage for white for all variations in the stockfish evaluation (up to +0.8 for white having 2 dark-squared and black 2 light-squared, and +0.2 for black being normal but white having 2 dark-squared compared to +0.1 for the standard start), but I'm not sure how valid this analysis is for an alternate starting position.

user14340: Are you familiar with the variant known as Crazyhouse? Basically, if you capture an opponent's piece, you can spend a later turn to place it anywhere you like on the board, as your own piece. This creates a situation where same-coloured bishops are possible, should you so choose.
The ability to create bishop 'batteries' can be quite good, presuming that you are leveraging your advantage on those coloured squares. Alternatively, if your opponent has a strong light-square pawn chain, adding more light-square bishops might have little benefit. This points to the answer provided by @HaukeReddmann - you are up on light / dark squares, and down on dark / light squares. You would need to analyze a specific position to know whether this is something you can leverage.
If you were to make such a change before turn 1, then you could also say that your development is already steered in a particular direction, meaning your opponent might be a bit more prepared for it, but that you might 'crash through' anyway.

user11144: And the correct answer, as always, is: "it depends on the position" :-)
OK, assume that you start with Bb1/Nc1. Lichess says +0.1. But this is the sum of...

the N generally standing a bit ugly on c1/f1, from my positional feeling
the B doing some concrete attacking (Stockfish unsubtly starts with c3)
other random concrete aspects
the question you asked: What is the isolated effect?

The isolated effect, of course, is that you are a whole piece up on all white squares, but down on black squares. GM Bangiev would rejoice: Adapt your strategy to be playing your dominance on white. (If that is possible.) For example, Bc4+Ng5 against short castling is completely useless. Fire it up with an additional Bb3 and Black already has a big problem.
Remember that different-colored bishops tend to be an advantage for the attacker, who exactly enacts the strategy I just described. (As the dude with the pair I of course would try the exactly opposite strategy - trying to get a position where both of your bishop just stare at pawns posteriors.)

20677: <p>Assuming one or both players makes a mistake and transposes a bishop and the adjacent knight when setting up the board, would this help or hinder them?</p>
<p>The answers to <a href="https://chess.stackexchange.com/questions/23252/are-a-pair-of-bishops-of-the-same-colour-usually-worth-less-than-a-pair-of-bisho">this similar question</a> suggest it's a disadvantage. However using the lichess board editor for different variations of this (one vs both sides with both on light squared or dark squares, etc) generally shows a larger starting advantage for white for all variations in the stockfish evaluation (up to +0.8 for white having 2 dark-squared and black 2 light-squared, and +0.2 for black being normal but white having 2 dark-squared compared to +0.1 for the standard start), but I'm not sure how valid this analysis is for an alternate starting position.</p>
 14340: <p>Are you familiar with the variant known as Crazyhouse? Basically, if you capture an opponent's piece, you can spend a later turn to place it anywhere you like on the board, as your own piece. This creates a situation where same-coloured bishops are possible, should you so choose.</p>
<p>The ability to create bishop 'batteries' can be quite good, presuming that you are leveraging your advantage on those coloured squares. Alternatively, if your opponent has a strong light-square pawn chain, adding more light-square bishops might have little benefit. This points to the answer provided by @HaukeReddmann - you are up on light / dark squares, and down on dark / light squares. You would need to analyze a specific position to know whether this is something you can leverage.</p>
<p>If you were to make such a change before turn 1, then you could also say that your development is already steered in a particular direction, meaning your opponent might be a bit more prepared for it, but that you might 'crash through' anyway.</p>
 11144: <p>And the correct answer, as always, is: &quot;it depends on the position&quot; :-)</p>
<p>OK, assume that you start with Bb1/Nc1. Lichess says +0.1. But this is the sum of...</p>
<ul>
<li>the N generally standing a bit ugly on c1/f1, from my positional feeling</li>
<li>the B doing some concrete attacking (Stockfish unsubtly starts with c3)</li>
<li>other random concrete aspects</li>
<li>the question you asked: What is the isolated effect?</li>
</ul>
<p>The isolated effect, of course, is that you are a whole piece up on all white squares, but down on black squares. GM Bangiev would rejoice: Adapt your strategy to be playing your dominance on white. (If that is possible.) For example, Bc4+Ng5 against short castling is completely useless. Fire it up with an additional Bb3 and Black already has a big problem.</p>
<p>Remember that different-colored bishops tend to be an advantage for the attacker, who exactly enacts the strategy I just described. (As the dude with the pair I of course would try the exactly opposite strategy - trying to get a position where both of your bishop just stare at pawns posteriors.)</p>
