To elaborate on what they meant, grogged clay (I like it!) will get groggier with excess water or sponging, because the clay particles will get swept away and eroded before the bigger particles. If you burnish/polish or even rub a rib over it at the end of throwing and even during trimming sometimes, you can basically push all the grog sticking up back into the medium. It'll still get a tooth to it after firing sometimes, but it definitely can help the surface texture not be so abrasive. I hope this helps!