35 mins is enough for regular travellers, but for some people it is not. So having 35 mins notice to offload someones bags etc from a flight rather than finding out 10 mins before departure helps the flight go on time.
Hence BA has some very good punctuality figures from T5 which in turn is a benefit to the regulars as they are hanging around less for those that can't get from security to the gate in 35 mins.