Information gets siloed in DMs. If I’m trying to find out why we made some choice in the past and try to search Slack for mention of it, it will not show up if all that discussion happened in your DMs.
Invariably, you will want to share the information in a DM with someone else at your company. Then you either need to copy the information out into a public place and start a new conversation. Or you need to add someone to the DM. But you may not want to add someone if you’re unsure anything in the DM history is safe.
Share any work information in a public channel instead. I believe in trying to make any work-related posts publicly.