I fly with the ‘world’s favourite’ (that isn’t anymore).
The general way of operating is ‘your sector, your PA’. However, if there’s some unusual delay going on, I’ll ask the Captain to make a PA as I think it’s courteous to passengers. Likewise, if I’m behind with duties, I might ask the Captain to make a quick PA while I’m finishing up.
Generally most Captains and FOs agree that it’s good experience for the FO to make announcements if it’s their sector. It’s another skill to add to the management of flying the aeroplane.
champ.