Why did you need to delete the message?
Some companies build it into their systems to automatically catch and mask that data, sometimes someone has to rollup their sleeves and do it manually.
I'd wager that 95%+ of orgs have tons of sensitive customer data scattered into chat messages in Slack, Teams, Hangouts, etc that would horrify most of us here.
Check out this: - https://cloud.google.com/dlp - https://www.youtube.com/watch?v=MY3PjFpI3rE
My least enjoyable job would be going into the admin to recover emails "deleted" by disgruntled employees who got wind that they were about to be let go. Why they tried to delete their emails - I'll never know. They should've realised that Google hates deleting anything from their clouds.
One of my happiest days at that job was the day I got told I didn't have to be a GSuite admin anymore and could go do some proper coding work instead.
Also consider that the first amendment isn't absolute and there is certain material that is highly unsavory, eg child pornography, that party B doesn't even want the potential of possessing.
There are certainly nefarious usages for that level of access as well, but I can imagine legitimate usage exists as well.