Just to clarify.


In the Key of C#. the note B# is essential as it is the 7th note of the key.

This is a useful distinction to make, as playing in the key of C# is a realistic and sensible alternative.




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.