Honestly? I don't trust Meta, but I like that they're implementing federation.
It will allow me to follow famous people or brands that only have a Threads account through the privacy of my Mastodon/Lemmy/whatever app, so I'm not forced to use Meta's official apps, which are famously riddled with trackers and whatnot.
Sure but then anyone whose ever interacted with you, outside of Meta, will be susceptible to Meta's privacy issues even if they block you or are only on instances that block threads because their previous comments will be on your content. At least from my understanding, that's how defederating and blocking goes. If I'm wrong, let me know but if not it's going to get hard knowing who we can interact with in the fediverse if they're also interacting with threads.