Errr, a lot of places have retention policies for chat, and that is a platform independent thing. After that retention time anything else is the same level of screenshots.

You can implement retention policies on IRC, slack[1], mattermost, hipchat, etc. On-prem / open vs hosted it doesn't change that.

[1] https://get.slack.help/hc/en-us/articles/203457187-Custom-me...