The object is to re-shape the plant, so mostly you either won't be removing the ties, or you'll wait until the plant is "trained" to the position you desire . . . at which time you could maybe remove them, but the branch(es) will reach towards the light . . . soooooooooo, if you've got your plant trained and your light(s) adjusted for that training, you can untie some of the ties.
As a rule, I leave mine tied.