Or situations where ones input is only valuable for a limited period of time or around a certain subject matter.
If it’s an hour long meeting and management or project managers have organised it - chances are I’ll have my laptop with me and I’ll be getting things done.
Of course I don’t turn up with my laptop open, not only would that be rude it would also be presumptuous as to the quality of the meeting.
However, if the content of that meeting turns out to be fluff - I’ll be working on being productive rather than watching slides of information that could have been emailed.