Except searchability of pinned stuff is terrible and often the only way to see the entire message requires clicking on it which "scrolls" up that point in history, incurring the CPU, memory, and network load of getting everything in-between. This is horrifying when you're remote working from a country with somewhat dodgy Internet connectivity. IRC takes almost no bandwidth and an IRC client takes minimal system resources, Slack by comparison is a hog.

Documentation in a Wiki is way preferable.