Drop tanks are a source of additional fuel for aircraft, at the cost of increasing induced drag and weight to the aircraft. Though, I suppose everyone in Aero knows that already.
For any aircraft that inherently possesses, or has opted to install drop tanks, should have their tanks ejected immediately upon complete expenditure of the fuel stores within, and thus loose the aerodynamic deficiencies.
Obviously, when aerial refuelling gets added (iirc planned?), you won't be able to magically grow new tanks just by getting fuel from a, say, KC-10, but refuelling on the ground will also provide the option on whether to reinstall tanks.