Hit the nail on the head. I even send emails summarizing hallway conversations I've had, just so there's a record of what understanding I came out of the conversation with. In part because ephemeral conversations (be they in person or over some IM system) often leads to misunderstanding and a summary can surface those misunderstandings, and in part to cover my ass when someone revised history.
It's not only to cover my ass but also to leave as many breadcrumbs in the trail to anyone that needs to read this in the future to understand what happened (including, most times, myself).
It's saved my ass many times and it's just a natural part of my workflow.
One organisation I worked for published the bonus scheme as a web page and I saved it and a year later when they were paying those bonuses they had changed the page silently without any notice it had changed. They refused to admit it changed when people called it out, until I provided the copy that matched everyone’s memory exposing management as liars. I was the only person that saved it, the workers were being short changed for £100,000s.