 
Making stuff into a drawing automatically detaches it from the grid among other things, but wouldn't it be great if you could then decide how translucent it is? So let's say the players discover an illusory wall and you a specific wall tile in place that you know is the illusory wall. Instead of having to remove it or mark it different or something, you can make it only 50% opaque etc. I'm sure there are likely other useful ways to use this as well but that's my main idea.
 
				
			