On BA short haul if you book a seat at the front of the cabin in Economy you get club class leg room. One less reason to pay for Club.
But those front rows are often not released to economy class passengers until very shortly before the departure date/time, at which time BA presumably has an idea of what the Club Europe loading will be. Which means that those who leave their online check-in and seat selection until the very last minute - often 12 hours before departure - can get the best seats. (At least, that's my experience on my weekly flights from City).