[quote name='Merton' timestamp='1349177373' post='1822734']
It's got something to do with using one control knob only, I'm sure.
[/quote]
Nearly - its all about setting the compressor up at the start so that you only worry about one control at a time, in a very specific order, making it far easier to hear the differences and make musically relevant choices.
You do in the end need to use all the controls to make a useable result, but at least you know where you are all the way through the process. Plus it helps massively when dealing with devices with poor or no metering.
Its a variation on George Massenburg's preferred methodology if I'm honest.