Don't know about you, but I rarely have much success fishing flats that are simply a sea of unbroken grass. Look for breaks or "transitions" including potholes of sand, places where one type of grass changes to another, edges, troughs, spoils, sandbars, oyster beds or even prop scars. I have heard it described as a "salt and pepper" bottom. It seems my biggest trout always seems to come from water so shallow that I can easily see depth changes, which, I think equate to ambush points. Areas where a predator can cruise, hide or simply lie in wait for a meal to make itself available.
I have noticed redfish, will slowly glide over a sand bottom, but when they get over darker bottom, which may be weeds or a slight depth change, they slow, pause or even settle in before moving on. Maybe they are searching those weeds for shrimp or crabs or maybe they are simply hiding, but either way, that seems to be where they want to feed.
Whether the fish feel safer with changing bottom contours or whether that is simply where they find their food, most of my casts will be to transitions that are visible.