Even though the question wasn't to me I'll jump in.
I sharpen mine using their abrasive power. Others with more knowledge can probably explain what's in it, but its an abrasive power that comes in different grits. I use a Shapton lapping plate, but another surface could probably do. The advantage is the lapping plate is it's flatness. I use the professional stones, but then I don't sharpen near as much steel as Steve, hahahaha.
The Shaptons are much harder than regular water stones, so flattening is needed much less. Harelson who imports them in to the US got me in the habit of using the whole stone for sharpening which also cuts down on the need to flatten.