exactly what its says on the tin

When a tree is removed you will be left with the stump slightly above ground level. a stump grinder has a rotating cutting wheel spinning at high speeds that shaves away the stump turning it into small wood chips.

A standard grind of 100mm below ground is plenty for grassing an area.the complete removal of stump and surface roots will be necessary when replanting in the same area or when building on a site.

This method is often preferred because it's faster and way less invasive than other techniques like digging up the stump.