You need to identify the thickness of the wear layer first. Know the floors specs and history before beginning sanding. If the floor has 2 milimeters left, it can handle light sanding of scuffs with a high grit rated paper. Always leave 1 millimeter of wear layer. So for instance:
2MM of wear layer can tolerate 1 light sanding
3MM can tolerate 2 light or 1 heavy sanding
4MM can tolerate 1 heavy sanding and 1 light sanding, or 3 light sandings
This assumes that you will remove 1mm of wear layer with light sandings and 2mm with heavy sandings. Consult a professional on site who can properly assess your situation and determine your options based on the condition and wood species. At some point, you will need to bite the bullet and purchase replacement wood when there is less than 1mm left.