All vehicles built since 1994 use automatic slack adjusters, which should self-adjust during normal full brake applications. If you find that an automatic slack adjuster needs manual adjustment to bring it back into spec, what does this most likely indicate?

AAMVA CDL Manual, Section 5, subsections 5.3.1-5.3.2, p. 5-6

Drivers sometimes manually crank an automatic slack adjuster to pass a failed self-adjustment check and move on, but that hides a real mechanical fault that will keep recurring and can progress to brake failure. Knowing this distinction protects both the driver's CDL and the public from a vehicle that should have gone to a shop.