I think it's very much culteral and specific to the organisation. Where I work now, hardly anyone has thier cameras on - except for some specific meetings that require it.
How is it different to being in a meeting room with people? Genuine question.
I find it far more tiring being on camera than not. In a meeting room you have a thousand micro private moments. Moments where you can see no one in the room is looking at you. Tiny fractions of seconds where you don't feel on show, using the feedback of being able to see where everyone is looking. In those moments, I could (for example) bring my slipping bra strap back up, fidget against my chair to scratch my back, maybe just slightly shake my head to keep me alert.
On video I never know where anyone is looking as so I never get those micro moments. I feel 100% permanently on display and if I need to do any personal adjustments I must do them knowing someone might just be looking right at my camera feed at that moment.
It's pretty small, but I think the culmulative affect is quite large - when taken over a day which holds maybe 4-5 hours of meetings (on average).
In addition, in a meeting room I can gesture a bit more, change position a bit more. Maybe even stand up for a bit of it - depending on the meeting. The people I am meeting with can all turn heads, chairs etc to look at me - if that's right for the moment etc.
On camera my posture must be a bit more fixed so that my head and face are 'in frame' for the vast majority of the time. People cannot follow my gaze around a room (and I cannot follow theirs) so I must behave in a way that keeps my face within the small frame of camera.
I think that's quite an unnatural way to spend several hours a day and find I get achey and sore from trying to stay so still. On the phone but not on camera (for eg), I feel more free to wander over to the sofa in my office for some of the longer one-to-one type meetings. I find the freedom to move and gesture with my arms (even though no one is watching) means my thoughts flow a bit better etc.