From a speaker view to 49 tiles
Speaker view, a 3 by 3 grid, 5 by 5, and the full 7 by 7 gallery. Each person picks their own; the host does not force a layout on anyone. On a laptop screen, past 25 tiles faces get smaller than a postage stamp, so the app suggests 5 by 5 there and offers 7 by 7 on monitors wider than 1920 pixels.
Tiles you cannot see are not downloaded at full resolution. Someone in a 300-person meeting looking at 25 tiles is pulling 25 small streams and one large one, not 300.