I’m not normally a fan of overhead joins, but there have been a couple of occasions recently (Henham Park & Project Propeller at Old Warden) where it has been useful in sorting out arriving traffic of radically differing airspeeds.
The usual caveat of checking Pooleys / VFR Guide / AIP and PPR applies. This will get you the information and probably the reason for any specific procedure. In the case of Headcorn you will be advised in no uncertain terms NOT to join over head…
Safe Flying,
Richard W.