But that's the way to do it regardless. You always want to work with a properly exposed shot. Trying to correct it afterwards, whether film or digital, often doesn't work. If it is exposed right, it usually makes everything else you do afterwards easier and the results come out best. What's the expression,
you can't make silk purse from a sow's ear. In my case though, since I'm shooting cheaper roll film rather than LF, I figure "wasting" a couple of shots is better than coming home with nothing worth while.
This shot
http://www.flickr.com/photos/alanklein2000/11854936794/in/set-72157626597775701 taken when the sun was setting was a little dark. But good enough to get a good result. But I totally blew the correct exposure probably because I forgot to release the shutter after releasing the mirror. But I was able to get the second shot to work although exposed slightly darker. There was another set of three bracketed shots taken right afterwards with a different lens that were all dark. So I lost all three but was able to salvage that one shot of 6 that I posted. For me that's great. One out of 6 seems good to me and worth the "waste" of film. Maybe the lower cost is making me sloppy, don't know.
But I think it mainly has to do with being accurate in your initial exposure. Often, it's not that easy. The light at this time of the day changes very quickly. You have to compensate for filtering, reciprical failure with the slow Velvia, etc. So even if you think you got the correct initial exposure, you might not. If you're shooting in the middle of the day, exposure readings are more accurate and consistent. Also, they're not changing from one shot to the next as they do during magic hour, before sunset and after sunrise. I shot one set of pictures that just a couple of minutes later were too dark just a few minutes later. Hey, I use to bracket 5 shots, so I'm getting better. Well, maybe.