I ask because some bikes don't like to be completely full. They will burn off some oil, perhaps down to the center of the site glass, and then stop. If your bike is one of these, and you top up every time you see the oil below the top line, you may just be burning that off.
This was my thoughts exactly. many motors like to be just a bit low. 1/2 a quart low on your bike should be acceptable.
Lifes too short to ride an ugly Motorcycle