Thanks to everybody who posted comments. I guess, I was mostly having
gaps in mind as I was posting my message. There are quite a few of
those in my apartment and I wasn't sure how to deal with them after I
sand the floor. Now that I know that boards are likely to expand as
humidity increases, I have a second thought about filling the gaps
with some kind of filler.

PS: Sanddust is the dust produced by fine sanding the floor once the
top layer is removed.