For many years I've been singing and playing in several rock bands but for the greater part happen to be very well received facing audiences. Up until not too long ago I might be inclined to choose songs that we performed based on how accurately we might represent that song from the stage. Which is, could we cover all the parts which make a song popular and get it done justice. Once in awhile a song will come along that required keyboards that were so important within the song how the song was only not worth learning to live without it. We would not be able to do it justice. So, instead of ruin the song we would put it on the shelf as a song we wished we might do. I did not see the sense in getting a full-time keyboard player to play in 20% with the songs at best so it made more sense to not do the song.
Because the time went on of course I joined a band that has been using backing tracks to pay for piano parts in songs and even complex backing vocals and instantly realized what those tracks can be worth to a performer. That resulted in the very difficult backing vocals could be spot on each and every time and the back up singers could sing easier lines when playing live, giving the rear ups a lot of depth. Additionally, it meant obviously that the music was greatly enhanced. The common audience member doesn't really pick up on a band using tracks. All they realize is band sounds much better than the band the other day but don't really know why. The answer then is in the tracks. Control singer can harmonize to his or her own voice more easily than another person can do it so he ought to be the one getting recorded. Take care not to put in a lot of though otherwise you risk the show becoming a karaoke act.
An important point to consider is what to do if you have technical problems. You need to have a way out. You need to know your show. I have been onstage and had the monitor system fail and not been able to hear the backing tracks and had to depend on the drummer keeping correct time. Using the tracks he's a click track in his left ear he should no less than be able to keep time. He provides the click from a pre-recorded track which has a click track on one side and the song sample on the reverse side. Using a small mixer on stage they can send the music activity the main mixing console and nobody in the audience will hear the clicking track.
Using backing tracks are a fun way to give your show an extremely competitive edge and hang you apart make up the rest of the bands in your circuit, area, etc. I am going to always use them now and am very happy to because all of the songs that I put on the shelf in the years gone by can now be done properly.