I wrote this out the other day in answer to a question on Twitter (thank you, Twitlonger!) and since my answer was over 3000 characters I thought I’d add it in here as well.
Batch processing in Lightroom can be done in a few different ways:
1) In the Library module you can use Quick Develop to make basic adjustments to one or multiple images. It’s important to understand one difference between Quick Develop and the Develop module, which is that Quick Develop makes relative adjustments and Develop makes absolute adjustments. What does that mean? Let’s say you forgot that you had set your camera’s light meter EV reading to -1, and made a series of images that are all one stop underexposed. What you want to do is increase the exposure of each image by one stop – no matter what the exposure was for each image – rather than setting the exposure for all of the images to a value of +1 EV. To make a relative adjustment like this you would use Quick Develop.
In Contrast, if you made multiple exposures of the same scene at different exposures and you want to give them all approximately the same exposure values, you would select the images you want, go to the Develop module and go to Settings/ Match Total Exposures. For more on that, see our Match Total Exposures in Lightroom post.