I have a 1 year editing window for registered members, and whilst I could change that for individual members, it would affect all of their content.
The case that prompted the suggestion was an otherwise very active and valued member of the community who had an image removed from their post that they felt should be allowed; they edited it back in again after it had been removed, it was removed again, and they edited it back in again.
I thought that it would be useful to be able to lock just that one single post so that they could not override the moderator action and put the image back in.
I appreciate that most people might resolve the problem by imposing global editing sanctions on the member but since I had the idea (and the feature doesn't currently exist) I thought I would suggest it.
It's possibly too granular for most people's requirements, may very well add unnecessary bloat; may even be better suited to an add-on; but it may also be something that is quick and simple to implement in the core ...