It has depended greatly on how complex the piece is, how familiar everyone feels they are with it, and how "natural" a feel we want. Sometimes a slight change in tempo is a good thing. Sometimes it helps to build the energy of the song (or bring it down a peg), and you don't necessarily want to lose that.
Most of my click tracking has been with bands other than my own when doing some studio work for friends.
I am neither for or against it. I think it has to be a decision made from the particulars of the situation.
One thought though...much folk music is traditional, and the folks who wrote those pieces had no click tracks...just a good drummer or rhythm guitarist, etc.