Well it depends on the setting, at a 1:1 ratio you are clipping the peaks and with higher ratios you are only curbing the distortion and managing it a bit better.

Another bit of advice I've recalled which many people take up, if you've done a mix and aren't entirely happy with it then you should sit down and do it again until it is right. I have the exact same problem with my mixes as I've got a terrible setup and some of the records I use have been mastered with different levels and stuff.