Are you saying they use the selvage edge itself?
I will use the selvage edge on a garment facing if it isn't puckered.
Or that they cut on the lengthwise grain (parallel to the selvage edge)?
Another "it depends on who is doing it" - I think it's Marti Mitchell that likes to make her first cut parallel to the selvage - I do, too, because then at least two sides of my pieces will be more or less on grain.