As I've heard Threads is not yet ActivityPub federation enabled- meta is going walled garden for the foreseeable future.

Benefits of federation would be:

• Massive available content boost for Lemmy, making user retention and growth easier.
• Much wider general user awareness of Lemmy and the Fediverse via federated content titles showing off instance names. May drive more natural user growth.

Cons of federation would be:

• Data security. it's Meta. Any and all user information, including admin data, naturally exposed by federated services instantly gets sucked into the Zuck data vacuum to build a user profile. Right now, we're still reasonably insulated from them.
• Spam. Threads is already massive by virtue of sucking in all the Instagram users. They would COMPLETELY drown any natural Lemmy content in their sheer volume of posts and votes, meaning lemmy native communities will struggle to gain any widespread traction over their Threads counterpart.
• Content manipulation. Anything Meta chooses to promote via their "algorithm" will end up on the top of every federated instance, meaning they can now effectively manipulate all Lemmy content by simply bombarding federated instances with whatever they want.
• Moderation. I'm not gonna sugar coat it, the average Instagram user is really dumb and it brings in all the shitty people with it too. Moderation of small instances will become impossible by sheer volume while federated with Threads.
• Principle. Meta's practices of extensive monetization and monopolization goes against every principle the fediverse was founded upon (freedom, decentralization, and emphasis on the user rather than the advertiser). By federating with Threads, you are giving Meta a free license to monetize the content you are paying to host on your own independent instance, for free. That just fucking stinks.