"Auto-Associate New User Via Contact" allows you to tell WebAlliance to look for a New User's email address in your ERP and automatically associate their Customer Code if there is a match. 

If you enable "Auto-Associate New User Via Contact" you can also enable "Auto-Approve New Users if Contact Found." This will allow WebAlliance to automatically approve any New User that is associated with your ERP's contact information.

Users that sign up without a Contact in P21 will still need to be manually approved. All Users that are automatically approved via Contact will be given the Default User Roles and Default Location for your site.

An alternative option to these settings are the  "Require Account Verification" & "Auto-Approve New Users if Invoice Verified" settings which can be used if you would like account creation to be restricted to customers who have an invoice from the last 30 days. There is more information on those settings here: https://wamanuals.aes2.com/m/21151/l/1278499-require-customer-verification-on-user-account-creation-add-additional-option