Finsbury Park is heavily used as a relieving point for Great Northern 717s coming in and out of Moorgate, and Thameslink 700s on the Cambridge-Brighton and Peterborough-Horsham services.
In addition, Stevenage is sometimes used as a relieving point on the 700s that go to/from Peterborough, particularly first thing in the morning or late at night. Previously a lot of hand overs happened at Hitchin before the May 2018 timetable change!!
Elsewhere on the network, despite having Drivers and Guards based nearby, Wimbledon on South Western Railway to my understanding is NOT used for relieving. The crews either travel PASS to and from London Waterloo for their trains, or work ECS trains in and out of the depot, although Durnsford Road staff halt is occasionally used for Driver changeovers.
By Travelling PASS it means walking to Wimbledon Park LUL, travelling one stop on the District Line to Wimbledon itself, then into London Waterloo by SWR!