[tars]

Then I don't see its use at all. Movie set doesn't support it, sorting by title won't be affected by that field, and sorting by sorttitle (if it's manually filled in) would only work if it gets auto-filled with title sortable when it's empty.

Edit: It may be useful if it works as a means to override title sorting (by title sortable) with manually filled in values, which is exactly what a sort-field does by definition.