You use of a screen protector, glass or textured plastic, is largely a matter of preference.
Some owners choose to forgo the additional physical protection afforded by a screen protector - whilst others prefer the reassurance of a sacrificial screen protector - these offering a significantly lower cost to replace than a damaged screen.
A tempered glass screen protector offers significantly greater protection from impact - and has a more slippery “feel”. Textured plastic offers almost no impact protection, but will provide some protection from scratches.
If used with an Apple Pencil, the plastic protectors will wear the Pencil tip considerably more rapidly.