The Delete Special command deletes not only the selected entities but their parent entities as well.
Caution: It is important to keep in mind that special-deleting a selected entity may cause many other entities (i.e. parent entities) to be deleted as well. Compare to the Delete command.
Note that a block entity is bounded by (i.e. "uses") domain entities which in turn are bounded by (i.e. "use") connector entities. Therefore, if you select a block, and then use the Delete Special command, the block, the domains it uses, and the connectors used by those domains will all be deleted.
When used on a database quilt entity, the Delete Special command will delete the quilt, its associated trimmed surfaces, and also its associated edge curves (usually hidden). As a comparison, the Delete command will only delete the quilt and its associated trimmed surfaces.
A special case is presented when deleting database entities that have grid entities constrained to them (review the On Database Entities section for more details). In this case, a dialog will appear stating that the associated grid entities are about to become unconstrained (see image below). The options in the dialog will allow you to decide how to proceed: