As with all these threads, bad practice is just bad practice. A good performer ( not necessarily the same as a good singer) can usually sense how much guidance the audience need.If they have already joined in some choruses with gusto, then probaly starting with the chorus wil be sufficient. If they are obviously not a knowledgeable crowd, sing something with a short refrain.
   You are there to entertain them, not show off your knowledge AND expect people to join in long choruses. I know several performers who think that they are God's gift to the audience. The problem starts when the performer thinks that the audience is God's gift to him.