Timbermate is a water-based grain-filler. Some woods are very fine grained and don't really need it, but others have deep grain patterns e.g. mahogany, and however hard you sand the surface, you'll always have loads of small pits in the surface. That mean any finish applied on top is going to follow those holes as well, and so won't be smooth. You'll then need to apply a lot of finish, so that you can get sufficient depth of finish to rub the finish back down so that it is nice and smooth and you can get a good shine.

Instead of that, by filling the grain near the start of the process, you can smooth the wood down so that you end up applying less finish and saving time. You can use a neutral coloured grain filler, or you can buy stained (or stain it yourself) grain filler, which will also highlight the grain pores if you are going for a transparent finish and you have a nicely figured top that you want to make the best from.