The main question about this is: Why on earth would you want to bother?

After all, "not having to fight for an overhead bin" is most unlikely to be a good reason for getting on board early, given how much space there is in the big bins and how seldom they are full in long haul economy.

Every minute not spent on board the aircraft before departure is an extra minute available in the shower, or sipping a G&T in the lounge. One of the greatest benefits of having lounge access when flying BA is the ability (aided by the lounge staff) of timing one's arrival at the aircraft just before they shut the doors.