One other note is that Facebook will handle a 1080p stream as input and will downconvert it to 720p for delivery to viewers. There's no real quality advantage to sending Facebook a 1080p stream and it will use more bandwidth than 720p, but there are still some reasons you might want to do this.
One is if you are doing local recording of a broadcast (for archiving or later editing). If all of your cameras and gear are 1080p, then you might want to run your switcher at that resolution so that the recordings are higher quality. And if you are streaming using OBS or other streaming software, this would allow you to do use a single output resolution (1080p) for both streaming and local recording. If you wanted a 1080p local archive while also streaming at 720p you would need to do multiple encodings which is significantly more resource intensive.
Another reason you might do this is if sending the same stream to multiple streaming platforms simultaneously, then you might want to send 1080p to the platforms that support it, in which case it's easier to send 1080p to all of them (to avoid the need for multiple encodes at different resolutions).
Also, Facebook has started to add 1080p streaming support to viewers as well, but it seems to be limited to gaming video streamers through their Level Up program for the time being:
https://www.facebook.com/help/publisher ... 0661747044And there are also reports that it is possible using a dedicated Wowza ClearCaster hardware encoder:
https://www.wowza.com/blog/1080p-facebook-live