DingusKhan: John Emad nailed it. It's a technique used for potted plants in nurseries. Perlite makes the pots really easy to move around. As Spidermite points out the trick is in the setup. Send too much water/nute solution through the cup and you'll have water roots follow the water out the weep holes, which is against the rules; too hydro. I write from experience on this. As for coattails, ideally, you'll want to let the bottom of the cup to dry out just a bit, without drying out the whole cup. So the proper watering schedule/flow rate is critical. On a large scale, see above for what the technique does to the root structure -- even though this is not a clone there is no tap root.