If not mental health, even just productivity suffers immensely... people with their eyes glued to the phone all day long just don't achieve much.
Not even at work.
I got rid of Facebook on my phone and don't feel the need to check it on my computer at all. It's a bit messy when someone wants to add me as a friend to see me on Messenger (literally the only reason I still keep Facebook—and I don't even like that—but Facebook is deeply useless to me.
I like Instagram for comics, meal ideas, and workouts. That's it. I think if you know why you want to use a platform and stick to that it makes it so much easier to limit your usage to reasonable levels.