While a polyurethane finish is not necessary, many folks like the satin or glossy look to their finished items. A few coats of polyurethane will give your item some protection from wear and possible water damage. Please note that a glossy polyurethane finish will give your item a smoother texture. Your wood-crafted item may lose that wood grain feel with this type of finish.

Glossy is easier to wipe clean compared to matte and satin.
If you need help deciding, please reach out!