The Split by Environment function allows you to split off grid cells of selected fragments that lie on the outside of the whole part.
For example, if you enter Environment in plus X = 2, all grid cells with less than two neighboring grid cells with a higher X-value are split off and added to a new fragment, no matter which fragment these neighbouring grid cells belong to.
Similar to the Create Hull tool, it allows you to create hulls or walls around a fragment. The difference is that grid cells of other fragments are also taken into account.