Talking with other people, having to be “on” and clever and think of things to say to add to the conversation can take us well away from what we should be focusing on.
Other distractions caused by our mics being on are background noise in other people’s physical spaces or just the time we spend telling other people “Hey, you’re muted. We can’t hear you” or “Somebody is listening through their laptop speakers, because I’m hearing myself twice.”
By keeping it chat-only we avoid being distracted by the (sights and) sounds surrounding those on the focus sessions with us.
The major benefit of body-doubling is that you are in a head space where you perceive that other people who are out “there” are being productive, so it makes you want to be productive, too.