If there's enough tape, it can prevent the compression nut from screwing down far enough to seal the joint. Also, stray bits of tape
can get lodged in the actual sealing surface, and cause a leak. There's really no need to undo a functioning connection just to remove
the tape, unless you're concerned about the reputation of the taper-upper. Thread tape is for use on tapered pipe joints only, where
the threads themselves are the sealing surfaces.