Pruning inactive/spam users
 

Okay, so apparently there are tons of users who have never made a post and haven't logged in for a long while so I'm guessing they were spam/inactive and stuff like that so we are thinking about pruning all these users who have never made a post.

1. What happens to user IDs of other users when all these users get pruned? Will their user IDs remain intact?
2. Are there any benefits of doing this action? This will decrease the 'total members' count by a significant number but will there also be any kind of benefits? Just wondering.

Not sure what you're asking here. But no, they won't stay intact - the users are deleted from the database. The id will cease to exist. If you're asking if that id will be used again (as in will vB fill in the gaps): No, it won't. All ids are auto increment. It's always last entry id +1.

Hardly. You lose a little of database size, but nowadays that just doesn't matter. Unless you're pruning really, really many users you won't notice a difference.