Can they? I don't really care, I don't use the corporate chat for personal things. I will act without regard to that, and if it comes to my knowledge that they did read them for the sake of controlling me, I'm going to fucking leave the company after talking to HR, that's an issue with the boss not the tool.

I do find that useful in a corporate scenario, where if someone leaves the should be able to retrieve all the information shared on those chats, and if you suspect that someone is saying things they really shouldn't to clients or colleagues, being able to check it is good.