"There are, however, no circumstances (that I can think of) where it would be necessary to play in the key of B#.

That would indeed be a nonsensical and pedantic distinction to make. "

Hah! Unless the key of B# is the 5th (V or V7) (or indeed any other related key essential for the chordal progression) of the Base Key of the Progression...

Not to count Modulations....

Sigh! The less people know the louder they have to shout the little they know!

Signed Mr Pedantic Trained in 5th Grade Music Theory ...
:-P