Some good points have been raised here ...
What I ask myself is "What is the expectation of the client?" ... If it is left up to me, then I would provide mostly instrumentals, with some 'low key' vocals thrown in, perhaps singing the song one time through after playing it as an instrumental, or even just singing the 'bridge' or a chorus ... Of course, I most likely would not do any vocal that is going to be a 'big production' number, unless specifically requested, and I would announce it as such ...
This type of gig allows the performer a great deal of flexibility in how songs are presented, i.e., adding or subtracting accompaniment, changing or eliminating tempos and styles, etc. ...