I saw a question regarding F# vs. Gb in a given song. The song began in Gb Major then went to F# minor . . . and then it was question as to why the change. Why not just write the song in one Key?
I believe it has to do with the flattened 3rd in Gb caused a problem in the writing. One would have a doubled flat for the third in Gb minor, which is played as "A" on the keyboard. I believe it becomes cumbersome to interpret the notes in the key of Gb major . . . so there needed to be a change to F# minor to make the reading of the music easier.
I hope I made my point clear.