The policy states:
How this plays out is if the member who creates a dupe is not banned we will merge the accounts and tell them not to do it again. If they did it again they'd probably get infracted or slapped, autoban is not the style.If a member with no previous offenses is discovered to have multiple accounts, he or she will be asked to choose one and the others will be merged into the main account. Members with previous offenses (including previous duplicate accounts) who create duplicate accounts will be subject to a ban, the length of which will be decided on a case-by-case basis.
If someone creates a dupe to get around a ban or potential ban due to having 3 infractions, that's when there's issues.