Nancy -- I often mention "routine" cleaning. I should clarify that. I don't mean regular cleaning, so much as I mean that the work that should be done almost always includes the same list of things.
With folding cameras, you usually will need to clean the viewfinder, clean the shutter, clean the lens elements, remove the old grease and then regrease the lens and reset the lens to infinity focus. If it's a rangefinder, you'll usually need to clean and recalibrate the rangefinder.
With camera lenses and rangefinder mechanisms, there is a single in-focus point for infinity. And you'll want both to be precise. That is, a distant object (1/4 of a mile) will be in focus when the lens and rangefinder hits its infinity mark. Not before and not after.
By the way, my favorite folding cameras are two very old Zeiss Ikons -- Ikonta 520/2 and Super Ikonta 530/2, a Super Ikonta 532/16, the Mess Ikonta 524/16 and the Super Ikonta III. All of them required varying degrees of service, but I expect this is a once-a-generation thing.