This filter is used to determine if the username/password account fields should show up at checkout. By default, it is shown when the user is logged out and not shown when logged in. The hook allows you to return true or false to override this behavior. If the fields are skipped while no user is logged in a username and password will be automatically generated for the new user after checkout.
apply_filters( "pmpro_skip_account_fields", bool $skip_account_fields, WP_user $current_user )