Sidechaning can add quite a lot to the clearness of the mix - when several instruments (f.e. bass instruments) are fighting for the same frequency, it's better to disable one of them when the other is playing. so far, so good, but it's also applied to other frequencies and more heavily than needed in the "french house" productions, which makes them really pumping - which is a whole different story again. however, if you just sidechain a bass and a bass drum, you won't even notice that the bass fades away!