Air mixture adjustments--what do they do?

[teazer]

t....Its to offer a slight adjustment of fuel/air mixture to compensate for such things as gradual seal wear.

Nope.  The pilot or slow speed air screw is adjustable to get idle and just off idle jetting spot on.  The pilot jet is so small that even a small change in air density is enough to require adjustment on the air/mixture screw.

Main jets air jets and needle jets are all replaceable but rarely need to be changed on a stock bike unless there is a significant change in air density say from sea level to 6,000 ft.

Just to completely screw with your mind, the air: fuel ratio changes as revs rise even at constant full throttle.  That's known as the fuel slope and can be changed by changing the air jet size or the height of the spray bar (outlet on a primary type needle jet).

Once you have the jetting right for your altitude and state of tune, the air screw would only need to be tweaked maybe in winter or heat of summer and even then, few of us would bother.  If a motor is badly enough worn that jetting needs to be changed, manufacturers would rather that you rebuild the motor, not mess with adjustable air bleeds that most of us would screw up.