According to the timetable, this service is set down only at Stoke, Macclesfield and Stockport so whether it is on time or early (depending on whether engineering works cause the service to maintain the timetabled arrivals), the train would not need to wait at any of these intermediate stations for the timetabled departure time but could charge onto Piccadilly and get in as early as it can.
I presume that's one of the reasons that it's marked as set down only. I think the last train west from Llanelli is similarly marked, though it never runs early!