When creating a new user on WordPress multisite there is a “Skip Confirmation Email” checkbox that is unchecked by default. This unchecked box results in a user being added to a temporary “signups list” when they are added to the site. The user is not fully added to the site until they complete the confirmation steps in the email they receive. For many sites, it is preferable to check this “Skip Confirmation Email” when adding a user. With some code you can set this checkbox to default to checked.