Posting chapter by chapter
In her post today, spikesgirl58 asked whether the writers among us post chapters of long works as they finish them or whether they wait until they have completed the entire work to post it all. I can see reasons for both practices. The thing that puzzles me is why some people post chapter by chapter when they already have the entire work finished. I don't think this is exactly common, but I've see quite a few works on AO3 with notes along the lines of "Don't worry, this fic is finished. I'll post a new chapter every week."
Have any of you done this? Why? If not, why do you think other people do it?
Have any of you done this? Why? If not, why do you think other people do it?