Aero mode even with ECO off?
If he did anything at all he is simply cutting power to the ASCM with his switch. So, as noted a nauseating number of times already, he isn't disabling Aero mode selectively--he's disabling the entire suspension system (i.e. "tearing the engine out to increase gas mileage"). This was in fact discussed as an option (not a GOOD one)...to which he said that wasn't what he would do anyway. So if that's what he did...we're back to that I suppose.
When it is left off is that when by accident someone hits one of the suspension buttons or power cycles, or the dealership does anything involving scanning the vehicle is when there will be unpleasant surprises. Plus, the longer you leave the system without power the more the air springs will become "unbalanced" and start affecting handling due to the lack of leveling function compensating for weight, temp changes, etc. In reading the air spring PSI with WiTech over a 25 mile run it's pretty interesting just how much the pressure changes simply from temperature shifts. In essence it's a very bad mod and not one I would recommend, if in fact that's what was done.