Used to indicate the opposite side of a matter: after mentioning a positive aspect, it points out the contrasting negative side (similar to 'on the other hand' or 'conversely').
この車は燃費が良い反面に、加速性能はそれほど高くない。
This car has good fuel efficiency; on the other hand, its acceleration performance isn't that great.
自由には責任が伴う反面に、大きな達成感も得られる。
Freedom comes with responsibility; conversely, it can also bring a great sense of accomplishment.
家賃が安い反面に、駅から遠くて不便だ。
The rent is cheap; on the other hand, it's far from the station and inconvenient.