Like what Gearbox said about dropping the external tanks when entering combat. Most external tanks are built to be retreivable and also refered to as "Drop Tanks". It was more-so on the prop fighters so they could go the distance on externals, drop, fight, then RTB(or other location). But having those tanks on creates extra drag which would be the last thing you want if you get engaged and need to avoid something/someone on your tail.
With the A10(any) it's already flying tank as is, anything to reduce that drag and allow less resistance and be abit more agile helps.
Besides, the last thing I would want to do is bring those fuel tanks into a combat situation incase a highpowered round does strike the tank and create an explosion of any sort. Any less hazard is a pilots best hope.