I still carry the rather 20th century idea that a performer of almost any kind also ought to have some sort of other talent in addition to their main one. The versatility of that sort of thing is one of the things that should separate a pro from the rest. I generally count "professional level musician" on more than one instrument as fulfilling that contract... perhaps one of the easier of the options, but it still carries that versatility advantage. Another example that I'm quite fond of is famous comedian Steve Martin performing Dueling Banjos with Kermit the Frog. The combo of two professional entertainers playing off of each other combined with the music skills creates the opportunity for a creative routine.