It would be a bit confusing - ie someone passing the ball to Longstaff thinking it's Shelvey expecting a 60 yard pass and getting a crap dribble instead. Or someone passing to Shelvey thinking it's Longstaff and expecting a short pass, and the ball being ballooned 60 yards and out of play.
I think Howe insisted on it after a scientific study shows it will lower his wind resistance and allow him to move quicker. God knows what Shelvey would be like with hair.