The layer for the SK Title Block. It has to be kept out of the way when you're not using it.
This layer is unusual in that it is hidden and unlocked in every output layer combination. There are no LCs of the form, A1 Floor Plan SK, A2 SED SK, etc. Since you might output an SK from any LC you would use for a CD drawing, we would need an SK LC for every current output LC. That's too many LCs for such a narrow purpose.
In practice, when preparing an SK, select the output view from the CDs viewset, then flip the SK Title layer on. (You can do this in the layer dialog, but I think it's faster to pick the layer in the info box, then respond to the 'that layer is hidden dialog after the first click.) Once you do this, you're no longer in an LC, but this doesn't matter when saving the view.