In our site, sadly some people create multiple accounts to usually create or "add more wood to the flame war" that complicates a lot the moderation because we can only check after the mess is done (because it must be manually done). People also use multi-accounting to get easy likes / trophies, etc... create Spam/PMs/Posts that they know that are not allowed.
How to be alerted or block users from create multiple accounts in the first place?
There existed one addon but it's abandoned sadly. Without it, all this announced moderation improvements are useless comparing to this lacky feature in Xenforo.