When not actively working with Design States, they can all be hidden instantly. Toggling will override the visibility of Design States so that none are visible. Toggling will restore them to their previous visibility, those Design States that were individually hidden will remain hidden.
Individual Design States can be hidden/shown in the Application Model View. You may want to hide all the Design States that are not related to the current task you are working on. Visible Design States will have an effect on the performance of the GDE Editor. By hiding Design States, the has less drawing to do, so it will be inherently quicker.