I typically use video chat apps like Facebook, Google Meet, and Zoom. I think the grid is efficient from a space perspective -- there's less wasted space -- but the grid looks very corporate and boring.
I think there's also a practical advantage of placing tiles haphazardly: it might help spatial memory. It's a lot harder to focus on or find a particular rectangle in a sea of rectangles than it is to follow a shape than looks a little different from the rest. However, I have never used FaceTime group calling (because I don't have most of my friends' phone numbers), so I don't whether this is effective in practice.
FWIW, I don't believe FaceTime requires others' phone numbers. I think it can be a phone number or any email address tied to their Apple ID, similar to iMessage.
I think there's also a practical advantage of placing tiles haphazardly: it might help spatial memory. It's a lot harder to focus on or find a particular rectangle in a sea of rectangles than it is to follow a shape than looks a little different from the rest. However, I have never used FaceTime group calling (because I don't have most of my friends' phone numbers), so I don't whether this is effective in practice.