We may also share aggregated or de-identified information with our partners or others for business or research purposes. For example, we may tell a prospective Slack customer the average number of messages sent within a Slack team in a day or may partner with research firm or academics to explore interesting questions about workplace communications. Again, this policy is not intended to prohibit the disclosure and use of aggregated or de-identified data.
All the communication made with Slack are saved on their servers in a way that they can have access to everything in a quite simple way (including conversation history, files…).
And to clarify the last sentence in bold, if I understand correctly (correct me if I'm wrong) : "this policy allow the disclosure and use of aggregated or identified data (with our partners)".