This sounds like advice specific for WFH, but it also applies to people working at the office.
The other person may be talking to someone else, in an unscheduled meeting, having a coffee, or simply have notifications off to be able to focus. I used to have them off for most of the day, and just check for messages at a half hour interval, otherwise it’s a total productivity killer. In a real emergency people will reach for a phone call.
As someone that has worked both remote and onsite customer service and tech it's kind of a wild difference. If I didn't flag myself unavailable or "sign off" even to take a short WC break it would start notifying supervisors of "not working", probably even worse these days with eye tracking and webcam monitoring of availability for the "not tech" crowd.
This sounds like advice specific for WFH, but it also applies to people working at the office.
The other person may be talking to someone else, in an unscheduled meeting, having a coffee, or simply have notifications off to be able to focus. I used to have them off for most of the day, and just check for messages at a half hour interval, otherwise it’s a total productivity killer. In a real emergency people will reach for a phone call.