Bringing your floor back to life...
Normal gaps along the joins in the floor boards can look good, but if there is a draught coming up through them then you should really get them filled. Wide gaps can be filled with strips of wood prior to sanding. Small gaps or slight damage like holes for pipes that don't exist anymore or an access hatch can be repaired with filler made up from the sawdust that came from sanding your floor.
Badly damaged floor boards can be removed and
replaced with new or old boards to match the existing floor.