When you link an account, it inherits the profile and verification level from your Primary Account. Your daily withdrawal limit will be an aggregate of all your accounts.
You can choose any of your accounts as your Primary Account, but you can designate an account as your Primary only once.
Account linking affects only profile information and withdrawal limits. Each account's balances, open orders, trade histories, settings, and credentials will be unaffected by linking.
Before you can link an account, your profile needs to be fully verified.