I too have modelling lamps, but often there's no model to point them at when inspiration strikes
I've been using this for a while -mainly to build shoot plans and work out the path of minimum light-stand and background wrestling to get through the set. I output the PDFs and stitch them into one PDF using Ice Cream's PDF merge and split tool. I then usually send it out to the model and rest of the crew. I also use it to present/teach - and to make diagrams for the blog:-
http://owenlloydphotography.com/?p=2496
It has a few glitches in it - never ever use the undo - it just does random things, and I wish it would output one PDF for the project and not make me type in the studio name, client etc on every shot but they're all small problems tbh. It doesn't do fog, or barn doors and sometimes you get odd lines or shadows that shouldn't be there, and I wish it would let me turn the speedlights vertical, but on the whole it works well, and as far as I can tell, the softbox light is fairly accurate - you can move it further away and get less fall-off, but harsher light, move it forward for more wrap, back for more edge etc. The only bit I don't think is too accurate is rim light when the light is behind the model, facing back to camera and hidden. It just doesn't show up, whereas in reality, it does... For someone who, like me, likes to plan an image and then go get the ingredients to make it happen, this really helps. It's also great for decoding light in someone else's shot that you like
