Sometimes when I am working in hand painted texture, I wanted to go in details and work on few uv shell at the time, but I am still want these details to be in one layer, without necessarily split them into different layers using masks and geometry mask.
A selection mode can be done as 2D software and selects uv shells that I want to restric, plus selecting geometry as geometry mask. This selection is a temporary restrictions for when going to details while people don't have to worry to paint over some strokes outside of the selected areas.