There is actually a tool designed to tighten and clip off wire ties. Being a retired phone man I am probably one of the few people that has ever used one. It clips it clean so there is no sharp edge. Believe me you can get cut on them. That said we always cut them with spicing shears and tightened them by hand.
I would be careful using them instead of a worm gear clamp or Oetiker. They don't always hold or have the same pressure all the way around.
EDIT: I forgot to say @wilcolandzaat that is a thing of beauty.