I've done that for years as well....especially if it's a high quality soap with a nice scent.Welcome to B&B, Sir Possum092!
I routinely use leftover lather as an aftershave balm!
After the shave, I'll squeeze out the lather from the brush and smear it over shaven face.
Let it sit for a few seconds, then wipe off.
The leftover lather leaves a nice glycerin-like film on the skin.
I'll follow that with a cool washcloth rinse and end with either a regular aftershave or a cologne.
Give it a try; it costs nothing!
Apply to face during clean up of razor and brush, putting deodorant on etc. Then rinse and do my post shave routine.