It’s generally excepted that it is easier to detrain at Harrow than it is at Wembley Park.
It’s better for customers as they have easier onward journeys due to the island platform 5&6 at Harrow rather than having to crossover from 6 to 5 at Wembley. The frequency of the services is sufficient these days as not to be inconvenient.
It’s also easier for staff as it means there doesn’t need to be a staff member on platform 6 at Wembley (which is often closed) and they can concentrate on dispatch at Harrow.
There are other pluses such as platform capacity at Harrow and the use of the fast line onto which out of service trains can wait without holding up the service.
Before the track work was remodelled south of Wembley there was an issues with track access to the depot clashing with southbound services but I think this has been resolved now (with some speed control?).
It’s just quite frustrating, particularly as they usually run depot trains down the fast, and Wembley gives you an opportunity to use the Jubilee or anything coming out the depot.
I was on the first off Uxbridge a few days ago & there was an O.N.A (train operator not available) to take the night driver off at Harrow N/B so the train was tipped out at Harrow S/B and we all had to wait 15+ minutes for the second train to come down. Whereas they could have run it down the local as booked to Wembley Pk and customers could have changed onto one that has just come out the depot with only a 5 min hold up.