The Symmetrize sop allows you to cut and mirror geometry along an axis. This is useful for making pieces symmetrical, or for creating cornerpieces from straight geometry like seen in the image below.
The direction / axis along which the input geometry will be cut and mirrored.
The origin at which the geometry gets cut.
Dissolve flat edges
Enabling this will dissolve flat edges in the geometry. This is useful for hardsurface models where the cutting plane from this tool has inserted a new edge.