It's good to clean your contact lists from time to time, remove old Nostriches that are no longer active, making room for new Nostriches to be added. Then, go find new Nostriches to follow!

What do I mean? Some clients and relays don't play nicely with very large contact lists. If you're follow 1000 npubs or even 1500 npubs, sometimes you may experience issues. Some clients and relays might truncate your contact list.

So, it's good to keep them clean. That's at least my philosophy.