It is completely private. You may be surprised at how effective it is. It is definitely better than no birth control at all. No fluid, or much less fluid, is deposited into the woman's vagina. This means that there is slightly less chance of infection spreading from a man to a woman.
Withdrawal causes no medical complications.
There are no hormones involved. No supplies are required. With practice, withdrawal may increase a man's understanding and awareness of his sexual response cycle. Couples often want to keep thrusting when it is time for him to pull out. This concern may decrease their enjoyment of intercourse.