The way you prepare the wood for finishing, whether by sanding as most do, or by scraping or planing as some do, has no affect on the way the wood will look with the finish applied. Different finishes add more or less color to the wood, but if you aren’t staining the wood, the way you prepare it has no impact on the appearance under any single finish.
Nor does the grit to which you sand the wood make any difference for the appearance with the finish applied. You can sand to120 grit or to 600 grit and you won’t see any difference after you have applied the finish.
This is somewhat counter-intuitive because the wood is glossier (shinier) when scraped, planed or sanded to a finer grit.
The way you prepare the wood does make a difference if you apply a stain, however. You should prepare all the wood exactly the same, meaning for most of us, sanding to the same final grit.
How to Know How Much to Sand
One of the biggest problems for beginners is knowing how much to sand to remove all the marks created by jointers and planers. Here’s a trick you can use to indicate when you have sanded enough.
Draw some pencil marks on the wood, then sand until these marks are gone. You could even do this a second time to be extra sure.
Use these pencil marks only when sanding with your coarsest grit sandpaper. Don’t draw the marks with the finer grits. Very little sanding is needed with the finer grits to remove the coarser grit scratches. It’s most efficient to sand out all the problems with just the coarsest grit sandpaper.