It would still need holding up (screws or whatever) - the gripfill wouldn't hold it in place.
TBH with a cordless drill driver the screwing is an easy job once you have the board up and in place.
I knocked up a couple of them out of bit s of timber
The tape reinforces the joint - otherwise it will tend to crack along the joint. Done properly - the tape is bedded in/covered with filler and then sanded so it shouldn't be visible -