Luxfer neut buoyancy tank advantage?

[DanL]

Very neat to have an AL tank that is not 4+ lbs positive when down to 500psi, but what's the difference from just adding, say, a 4lb tank wt to a regular AL tank?
The Luxfer site lists the following wts for a reg tank and a NB tank:
Empty weight (actual) Empty buoyancy
S080 31.4 4.4
S80N 35.4 0.05

The NB tank is 4lbs heavier to begin with. Wt dist is an advantage perhaps, but again - why nit a tank wt?