Refeed is to replenish leptin levels, which in turn help keep metabolism churning. It may also help metabolism completely independant of leptin levels as well. T3 simply raises metabolism artificially so when you come off of it your metabolism will at best go back to what it would normally be, if not lower. If you're in a heavy diet cycle and in a severe caloric deficit then my guess is that stopping the T3 will bring your metabolism down to where it would have been sans the T3, which needless to say would be in the dirt. I'd say do refeeds regardless of T3 intake that way when you come off of it you have a better chance at a normal metabolism. Don't be scared of refeeds they won't hurt your progress unless you manage to become a gluttonous fool who sucks down 8000 kcals of junk.