Of course, all of my crowd thought I was a jealous musician and wasn't telling the truth (including my wife.... ha!) until I had them watch the bass player while listening to the bass line. He was singing lead. So, like some old country singer who strums a chord or two between vocal lines, he "played" when it was easy. Of course, they were all offended at that point. And the same band became cheesy to them. But up until that moment, they were blown away by the band.
I pulled the same stunt one time about 15 years ago when I did a "pickup gig" and didn't know a particular tune that well. Fortunately, we only did a few tunes where we used backing tracks. I still feel slightly tainted about doing it to this day. Personally, I would rather fake the tune in the right key than play along with a backing track that way.
That said, some bands integrate them tastefully. When more than a small percentage of the music is generated by them, however, the life often gets drained from the performance.