Ratcheting is a technique used by mtbers to get through and around obstacles when one doesn't have room to make full pedal-strokes. It can also be used for water short water crossings when you don't want to get your feet wet
It's not just a matter of room to do a pedal stroke, it's used when a full pedal stroke would take you too far, give you too much power. Or where you need more momentum than you will get from coasting, and you can't control your speed with brakes, or just balancing.

What is it anyway? It's little movements backpedaling or "racheting" just a little bit, then applying just a hair of a pedal stroke, rinse repeat.

Now, I don't know about road biking, but when manuvering around very tight obstacles on a MB, you should be out of the saddle in a neutral position, and pedal level ( 3/9) and fingertips on the brake lever.

Let's see how long I can remember all this stuff from camp... ;-)

Irulan