Before digital photography, the best way to test your lighting was with a Polaroid film back. Medium format cameras would make Polaroid film backs so that you wouldn't have to waste film, time or money on making mistakes. Mostly used for studio photography, it made perfect sense. From my little experience of studio photography, I noticed that it was the setup and lighting that takes the longest to get right, so the 'practice' shot with your Polaroid back was essential.
Fast forward to now and things are a whole lot easier. After figuring out where my flashes are going, a quick digital test shot and we're good to go!
More often than not I shoot a digital test photo and get really hyped on it. I usually think to myself "maybe I should shoot more digital?" Then I get the film developed and I'm reminded why I don't. Having said that, I don't have the latest gear so that may have something to do with it!
It's interesting to see the difference.