For the purpose of understanding the required surface smoothness of bare wood before a finish is applied, we can divide finishes into two groups: waxes and lacquers. The wax group also includes, with some reservation, oils. (Modern oils dry hard and quickly and are capable of a high buildup compared to earlier boiled linseed oil products. Multiple layers can build to a point where they become comparable to lacquered coats. However, one or two oil coats let you feel the wood surface, like wax.) The lacquer group includes lacquers, conversion varnish, water-based finishes and the like.The main difference between the two is the amount of buildup left on the surface.
The buildup on a waxed surface is negligible, so the tactile quality of the surface should match the smoothness standard you want, from either handplane or sandpaper, before you apply the finish. When you touch the work, your fingers are on a waxed surface, but that surface will be as rough or smooth as the wood beneath it. Hence the requirement that it be handplaned or sanded to 400-grit.
When using a film-building lacquer, it’s unnecessary to sand finer than 180-grit.That’s because the surface of the wood is entombed below the lacquer thickness. What you feel when you touch the workpiece is the hardened surface of a chemical above the surface of the wood.