how secure is Identity-Safe Log-Ins?

The intent is for --- what?--- convenience, or for security, the Identity-Safe Log-In combinations, the feature found in both Norton Internet Security and Norton 360?  How safe and secure is this Identity Safe feature?  How do we know that during any website searchs and visits we would not become accidently infected with something that breaks through to find our log-in information to some of our chosen websites/webpages for which we have usernames & passwords?