In the time it takes to load one figure and pose it decently (much less a whole composition) you can do a dozen thumbnails. And for each thumbnail, you not only solidify the idea you have in your head, but also figure out a plan of action, see any problems you will run into and have a guide to refer back to when you do start working in 3D. You can also show the sketches to other people to get feedback (very important in a commercial project) and quickly make any changes. ie pencil thumbnails are a well tested and practical method of organising your thoughts in a form that is independant of your own inner eye.

Really, i see no reason why anyone would not do a bit of sketching before starting the 3D. At worst you will have wasted a few minutes and at best saved yourself a lot of hours of wandering around blindly doing poser doodles.

Plus drawing is, you know, fun ;)