He will normally use the maximum amount of pavement available.
Well, this doesn't appear to be a rule of thumb applied by all easyJet, Ryanair, Wizz, Aer Arran, FlyBe or bizjet pilots operating at Luton, and it often helps
them to avoid additional delay so it's not just a matter for the airport's flow rates (important though, they are - to the airlines).
Neither is it religiously applied by Aer Lingus, BMI, BA, etc., etc., short-haul pilots at Heathrow.
Ditto many pilots/operators at Gatwick, Manchester, Stansted, etc.
I always thought it was something called a "Balanced field take-off" and - provided the figures and Ops Manual permit it, then it's both legal and safe.
And before someone points out that the runway length at Luton is rather less than at these other airports, this is
not the issue if the aircraft commander is applying his/her company procedures and has determined that the 'figures' will permit it.
Anyway, in days gone by I've seen many a long-haul 747-200 struggling to make it out of Heathrow and Gatwick on a summer's day, even with 3000 metres.