The advantage of push-to-talk is that you are muted by default (necessary for large groups), and the app knows when you want to talk because you have to push the talk button. That is extremely valuable information that you can use to build other features on top of. For example, there's no need for a "raise hand" button anymore, since pushing the talk button clearly signals your intent to speak. The UI can highlight your square, make it larger, whatever, which can make the whole experience a lot smoother.