For myself I like to have the printed sheet music for a song in a least 3 different keys before I sit down at the keyboard and start to arrange a song.

Many of the instruments on the keyboards sound their best in certain note ranges, and of course in trying to put them altogether in a harmonic structure, certain keys will work easier and better then others in different combinations.

Not having different keys to work with would, for me, be boring and non productive.

Larry Gosmeyer