Almost every woman has some slight difference in the size and shape of her breasts. You are correct, 25cc is very little, but since implants are not packaged as pairs, we can choose implant sizes very precisely to give the best possible symmetry. Think about shoes, wouldn't it be nice to be able to buy one shoe that is a half size different than the other- it may not be much, but may fit better! Good luck
Most women, in the preoperative state, have breasts that are different in size and it is quite common to use different sized/filled implants to even things out. 25 ccs may sound like a lot but it amounts to less than a shot glass. Hope this helps!