The idea of balancing your rig has 2 major advantages. One is that if you have to doff/don underwater (serious entanglement, etc.) you are roughly neutral rather than having to hold desperately to your rig to avoid corking. The other is that it is not uncommon to doff your gear at the surface for convenience (some boat crews will let you pass it up rather than climbing the ladder with all your gear, etc.) and regardless of reason, if you doff the gear at the surface it has to be able to float itself.
Respectfully,
James