When vertices are selected, Detach Component separates any selected vertex that is shared by multiple faces into multiple vertices depending on the number of faces the vertex shares. The edges of the faces associated with the vertex also become unshared as a result.
When edges are selected, Detach Component separates the selected edges into two overlapping edges. If you perform a Detach Component operation over a path of edges, the vertices along that path are also seperated along that path. The vertices at the ends of each selection remain attached to both of the new edges or edge paths.
If both vertices and edges are selected, Detach Component defaults to the same behavior as when only vertices are selected.
+ 
when the polygone is in Edge mode.