Sanding sealer not always necessary, always optional! Sanding sealer's primary use is level surface of wood and speed up surface build of final film finish.
Contrary to what manufacturers tell you sanding sealer poor wood grain-pore filler. Just use any film finish for that purpose. Can thin any film finish to act as sanding sealer commonly called a wash coat to serve same purpose.
On porous or open grain wood better to use several thin coats of finish, allow each coat to dry completely. Do not forget dry time between coats not the same as final cure time for a finish. If try to rush things going to end up with gummy finish.
Sanding sealer not a final finish, dries too soft.