most of the lemmy servers block threads outright

Lemmy does not display microblogs, which is what Threads is.

The only way we’d see content from Threads here is if someone on Threads somehow stumbles over content from here (for example if it’s boosted by a Mastodon user they follow), and leaves a comment.

That, or if Threads users tag a community, in the same way Mastodon uses can do.

Basically it expands the theoretical reach of the comment section, but in practice it’s unlikely to have a huge effect.