For my 12x16 or larger pieces, I tend to do at least a couple of layouts prior to committing to the actual paper. For all cover and sequential work, layouts are critical, and it just makes sense to carry the practice over to commission work. In the layout phase, things like composition, lighting, juxtaposition, sight lines, etc can be easily figured out before getting into the weeds of a piece. A piece can become very flawed if these things aren't worked out ahead of time - and on even a thumbnail size image. Take the two images above; Each in my opinion has merit and often if I like both pieces, I give the choice of which to take to final to the client or commissioner. It gives them a chance to be part of the process, and makes the piece that much more personal to them.
Sometimes the client doesn't choose the one you expect, so make sure you enjoy both layouts if you give them the option. This Gotham by Gaslight Batman was the one the client didn't choose. It also helps to explain the layouts sometimes - to clarify if your layouts are extremely loose. I do this often with my layouts for comic work in particular. See below my layouts for an issue of Lovercraft:
You'll notice aside from just notes, I have color coding to make things easier to read quickly and understand who is talking to who. My comics layouts tend to be very loose and quick as I do an entire comic's layouts in a day or two, and when you get into a rythmn pf working with a particular writer it becomes easier to understand what's being conveyed. These layouts are about 2.5x4 roughly. Also notice my little overhead layout scribbling to the left of page 4. Stuff like that is how I work out character movements in an environment.