As part of your “entry” into service (in the USA, in to the Air Force, during 2004), you pay for three haircuts. That means you are getting three hair cuts.
If you show up and don’t “need” a hair cut, they’ll go ahead and snap on a guard to their clippers and run it over your head anyway. Again, you paid for a haircut, you are getting a haircut. “Need” is not a factor here.
From what I heard from the two guys in my unit that tried to “beat the system” this way, a clipper cut on a bald head is quite uncomfortable. They wouldn’t recommend the experience to their friends.
Oh, and one other note. The barbers are not likely to be like the lovely lady you see in the picture above. They aren’t going to be “gentle” with you. If you have a head of hair, they have a job to do, and they will do it quickly, but professionally. If you don’t have hair, they don’t really have a job to do, and that is likely why the “haircut” gets a bit uncomfortable.