I signed up to Quora with my Facebook account, back in the day. Deleted Facebook in 2013 and lost access to my Quora account, with no possible way to recover it.
I haven't used a social login since. In my case, it was fairly harmless, but it made me realise how dangerous social login is. Every time there's a signup, I look for "signup with email". It's the safer option. And if you can, use your own domain for email (Google's paid email offering supports this, as does Fastmail and countless other email providers). That way if your email provider decides to flip you off, you switch DNS records and you're up and running somewhere else, and everything keeps on running.
But: If you don't have a copy of emails then you lose all saved emails, so make sure you have a backup strategy in place.