Unless I'm firing off a quick reply I normally compose post/replies offline in notepad with quotes & links etc. That way I can take my time with a subject while researching it as well. Then it's just a matter of copying and pasting and letting the spell checker do it's thing, hitting the 'Preview' button and re-reading to make sure it flows the way you want etc.
If an error occurs, if I'm incorrect about something for example, I'm sure someone will point that out and so be it. But as threads grow, you'll still have to make an extra post just to say you've changed a post some 12 pages back. Considering the length some threads and individual post can get; I'm not sure every interested party will go back and re-read a lengthly post, in a lengthly thread to check out that clarification.
Unless one is using the forum to 'store' their growth in relation to a particular concept, which isn't necessarily it's function, I'm not sure why unlimited editing would be of any value. I can especially remember a couple of threads wherein I made some errors and with the help of members over the duration of a thread you could 'see' the working out off the kinks in my faulty logic and/or failed premise. That was great stuff. Taught me to be a bit more careful, cautious and to research as much as I could beforehand.
Also. You guys do realize that there is a 'Save' button when composing a reply or post. It 'Saves' the post into a 'Draft' folder. You can edit it until comet Holmes stops discharging (whenever that will be
) without actually posting it at all. So if you want to use post to 'store' ideas etc that's one place to 'store' and 'Edit' to one's content.