Foliage - how does Erase Density work?

How does the Erase brush / Erase Density work when using Foliage Mode? I don’t get it.

Paint trees and set Paint Density 0 - 1. Ok, I get it. No forest or thick full forest
.
The same doesn’t seem to apply to the Erase brush / Erase Density settings:
Only Erase Density 0 removes entire forest, anything above 0 value does absolutely nothing.

How would I “thin out” a forest if the Erase brush just removes everything?

Anyone? Please?