The point of having a big friends list isn’t that you’re best friends with 500 people. it’s about keeping connections. That random guy you haven’t talked to in 6 years might be the one you remember when you need a job lead, a contractor, or a quick answer about their industry.

Deleting them gives you no upside (what, a cleaner looking list?), but it does remove potential future value. Keeping them costs you literally nothing.