Filling in the gaps can be very beneficial both in terms aesthetically & to keep out the cold draughts during the winter months, which means less heating costs overall & in turn increasing the heating within the room(s).

 

There are two options:

 

Should the gaps between the boards are of 3mm or less this can be filled in by mixing the dust that was previously collated when your floors was sanded then mixed to a paste with Bona resin & spread over the boards. The other option should the gap(s) be wider than 3mm would be to insert & bond in reclaimed slivers, as you can see from the pictures below.