I could understand the decision in the Nine revival as a way to get the rest of the cast to sound like they were in the same world as Antonio Banderas who (presumably) couldn't do an American accent.
Another weird example was Women on the Verge ... why did an all American cast, speaking English, and performing for an American audience need Spanish accents??? (In the book Here's to the Ladies, Sherie Rene Scott says she asked the creative team this question during rehearsals and was told the jokes were funnier with the accent.)
