As an addendum to this idea, I'd love if depleted ammo cases could not only be dropped, but cause a small (depending on ammo type and mech, of course) increase in overall speed. Consequently, electing to not "fill up" on ammo when purchasing a mech/tank could be a tactical decision to maximize speed.
I won't speculate as to how difficult it would be to implement such a feature, but I think it would be an awesome little detail to add. Lightly armored assets like light mechs, harassers, and smaller aero units would appreciate it (especially if we come late in the game).