We are in the same predicament. The experts vary on this subject but overall the concensus was that with the contraction and expansion of wood you will have gaps. Of course large gaps should be filled. We bought a product that you mix with the sawdust off your fine floor sanding. It did not work well as it dried way too fast to be flood filled in the gaps. Our local flooring man who has done this for years used drywall paste mixed with brown tint? He said he had done every type of product available but this worked for him and shifted with the weather changes. It's a stretch to imagine and since we have not applied this yet you might ask your local flooring installer for his opinion. Other than this Pacific Filler makes a product that you mix with water and flood fill(trowel over the area in all the cracks) the gaps. We did not have a local source for their product. GOOD LUCK and hope this helps.