If you remember from your high school drafting days....and my days working as a machinist, as you continue to look over the print you find details that you missed or dimensions that you need or will help clarify the part. Anyway....as I continued to work on the print I had to add locations for screw holes and supporting dimensions in order to have a good print.
I remember as a machinist having to contact the engineering department at times for missing dimensions or information....blueprints require a lot of detail and they can be missed only to be found when the person making the part lacks information for making the part!
So as I completed the print there was a lot of review and tweaking items.