LinkedIn isn’t a terrible idea if you just want to come up in search results. It’s quite useful for a lot of different professions for networking. You’d likely just make a profile and never look at it again.
Facebook can be almost mandatory depending on where you live. I currently live in a city where Facebook is the only meaningful source of networking, local news and information on events online. It’s not uncommon for businesses, even quite larger ones, to have their only media presence online be a Facebook page. The city is also kind of infamously hard to break into socially so you want any advantage you can get.
I don’t currently have any social media but it’s become a hindrance and I might need to reactivate. I end up using social media by proxy through family and friends anyway.