Cat grooming after abdominal surgery

Two weeks ago my cat got an abdominal surgery to remove 2 large hairballs, one in the tummy and another in the intestines (that had completely blocked up everything).

Dude has a sizeable scar afterwards. Today they removed the sutures. Is it safe to let him groom himself freely, even licking the supposedly healed incision?

My veterinarian said its okay as long as he doesn't overdo it but that seems very open to interpretation as in how much is too much or if I should even be worried at all