It will make login faster and easier with Facebook, Google and Twitter.
Why add Social Login to your Shopify store?
Customers hate creating accounts and having to remember usernames and passwords. This is the single biggest dropoff step for your store.
With Social Login, customers can log in with their existing social identities. By avoiding existing registration and login procedure which is slow procedure it's an opportunity for increased customer conversion.
For Shopify Plus :
Multipass login is for store owners who have a separate website and a Shopify store. It redirects users from the website to the Shopify store and seamlessly logs them in with the same email address they used to sign up for the original website. If no account with that email address exists yet, one is created. There is no need to synchronize any customer databases.