Nothing is as frustrating as looking for an old conversation referenced in a doc and being smugly told by some corporate dick that Slack isn't for documentation and if it were important info, clearly someone should have saved it. Never mind who, it should just magically happen.
The gap between "messages last for 30 days" and "Slack keeps a searchable record of all your business decisions in a useful way, forever" is huge. I can pretty easily see the value of the latter but it seems to freak executives out for some reason...
That doesn't track with my experience as a user at all. Almost every day I do a search that returns results older than a year.
I find that this take is much more common among managers and executives who are used to being spoon-fed documentation than among the engineers who actually have to write and hunt for it.