Don't forget that not all start and finish aerodromes have ATZ's.
I was flying (my glider) from Aston Down (unlicensed, so no ATZ), recently. Not only were there events at Kemble which one could be very close to, there were several days when South Cerney had a parachute drop zone 5nm radius and 12000 feet high, which overlapped Kemble's ATZ and came close enough to Aston Down's downwind area for gliding there to need to be very careful (not so close as to affect the circuit, but certainly affected local soaring). A narrow route from e.g. a gliding site in North Wales to Aston Down would not have picked up that NOTAM if the system does what it says on the tin.