no no that's not at all what he means...
if you hit a bump in the road at 50 mph, that's a sizable impact. If the bike is dropped too far, it really won't take much at all to get the rear tire to touch the undertail. Like we're only talking a couple inches of travel here. Better to be safe than sorry
so your bike doesn't end up looking like this one
Don't go past 1.5 inches. That's the lowest you can go where the rear suspension can still go full travel and not rub the tire on the undertail