The hinges where designed for water based wood glue.
You drill a hole just big enough for the hinge point to go in.
You put in a drop of wood glue then insert the hinge.
The wood absorbs the water in the glue and swells around the hinge point.
The glue dries and hardens the wood that is now pressure fitted around the hinge point.
Any water based glue that got into the hinging part it self breaks free because the wood glue doses not stick to plastic.
No need for grease.

Now some people don't trust water based wood glue and use epoxy instead.
Epoxy sticks to plastic really well.
So you need grease in the hinge to keep epoxy from getting in it.

If you follow directions then you will not need grease as you will be using water based wood glue instead of epoxy.