I worked in an antique refinishing shop long ago. Every piece of furniture we refinished would be sealed with shellac as an insurance policy to make sure the old finish, if there was some still hiding, would not interfere with the new topcoats and sanding sealers we used.
Shellac is an amazing sealer that is very forgiving in the event that there is something on the wood that would cause the lacquer to have issues with adhering. It also dries ridiculously fast so you can build up coats quickly, and it sands smoothly. Lacquer also sands nicely, but in my experience it takes longer for it to cure before you can give it a good sanding.
I have done a few items using shellac as a sealer and topcoat and they come out looking great, the only issue is shellac will come off if you get alcohol on it so thats why I top my racks with lacquer.