Should I reply to old Facebook friend requests?

It depends on who they are and how you feel about reconnecting. If it's someone you genuinely lost touch with and wouldn't mind hearing from, accepting costs you nothing. The worst case is they don't message you anyway. But if it's someone who made you uncomfortable or you have no real connection to, there's no obligation. You can just ignore it indefinitely without guilt.

The tricky part is when you're unsure. Sometimes I've accepted requests from people I vaguely knew years ago, and it's been nice catching up or at least seeing what they're up to. Other times it's awkward and we never interact. What I wouldn't do is accept out of politeness if you actively don't want that person in your feed. Social media is supposed to be your space, and you get to decide who's in it.

If you're genuinely interested, accepting is easy and low-stakes. If you're hesitating because you feel obligated, that's a sign you probably shouldn't. Facebook doesn't notify people if you decline anyway, so there's really no social consequence to just deleting the request or leaving it hanging.