A closed door isn't always enough. A booked video call stays fixed in your calendar: if someone else books the same slot, you work connected. The same idea as coworking in an office, for people who work from home.
People who work from home often have more distractions within reach: not just the phone, but the rest of the house asking for attention too. Closing the door helps up to a point: the decision to stay with the work has to be made several times a day.
A booked coworking slot is fixed in advance: at the chosen time the session starts, and if someone else booked the same slot you are connected together, at the same time for both of you.
Yes, you can leave whenever you want. A session left halfway doesn't count, though, and the other person is left alone: if you know you might have to get up, pick the 25-minute slot instead of the 50-minute one.
No, a device with a camera and microphone is enough: the session works from any room.
Yes, for the whole session: there is a button to switch the camera off for a moment, if you really need it, but the session happens on video. You don't have to show your face, though: you can point the camera at your desk and show that you are working. If you prefer to work without a camera, the timer and the “Solo” mode open no video call.