I'm referring to Evocación, the first movement of Iberia, which is in the key of C flat (7 flats, every note flat). The key of B uses exactly the same hotes, but using 5 sharps instead of 7 flats. To the listener the C♭ and B keys sound identical. 5 sharps are easier, one would think, to deal with than 7 flats. The meaning of choosing C♭ over B has nothing to do with the sound of the piece, and it makes the work harder notationally for the performer. There is a message to the performer (who is the only one who would know) in the choice of the C♭ key. If you can't play this key you shouldn't even be looking at this piece? Flats are more dreamy, but sharps grate? For the performer only? Commentary welcome.
I'm a pianist, and have performed this piece, for myself only, many times.