This solves the problem of deleting implicitly child-items, which depend on each other when deleting an item. When deleting an item, the deletion of child-items in the content repository happens in an arbitrary order, which could raise fk constraints. Since the deletion happens in a transaction, the deferring checking of the constraints helps, since then the constraint violating item is also already deleted.
There is no update script necessary, since reload alters the constraint.