Many moons ago, the British Midland Viscounts (at LBA) frequently used to start the two inboard engines on stand, taxi off and then crank up the two outboard engines whilst approaching the holding point, something I never recall the BA machines doing in the 70s.
Not that a Viscount is an A320 (although they sound uncannily similar when flying overhead) but there's probably a common reason behind it all.
Any ex-Viscount jockeys care to comment
Mooncrest