Great point, Jerusha. At the same time, playing what we think of as timeless standards for younger crowds might not produce the song recognition and response we expect. Over time you learn how to read your audience and adjust the music as needed during the gig. This is why I love playing from a ipad. Very easy to change up the set list at a moment’s notice.
Similarly, playing religious music can either be the best thing and bring tears to people’s eyes or the worst thing and offend people. For a background gig or anything where music choice is loosely defined (think “easy listening” “classical” “love and pop songs” or that oh so clear “mix of whatever sounds good”), I ALWAYS ask the client during the initial consultation if they would like religious songs included, excluded, or if they have no preference. Takes the guess work out of it.