Be careful:If Jan does this all those who already have printed with the "fit-to-page"-option on will have done this for nothing...
Uhm - no, those would not be harmed. The "fit to paper"-option scales the whole A4-sheet down to fit into the printer margins, no matter how much white room is on the edges. If 2 mm or 2 cm: It doesn`t matter.
You WILL have, of course, a problem if your printer get's a defect or so and you`re forced to switch to a new one: You will have no idea what the scalng ratio of your original was and will have to do a lot of try and error with a new one. Remember: It may take a while until the model is complete!
So a variant that will print on most printers without the need to be scaled would be the safer way.
That`s why I suggest to leave approx 3 mm on all edges free, that way it would print nice on many modern printers without to be scaled. Once again: If you use the "fit-to-page" option pages with such a layout will have the same ratio like the printed ones, so no problem for those fellows.