Single sign-on ("SSO") is a service that makes it easier for your employees to access the systems they need to do their jobs, without having to maintain separate usernames and passwords for each system. Your Security team will appreciate knowing that there are fewer passwords floating around, and that it's easier to control who has access to your Recurly data.
Recurly's support for SSO uses SAML 2.0 to provide full support for authentication scenarios where employees login to your chosen "identity provider" (e.g. Okta), and from Okta they then access Recurly. Once your employee is logged in, they get access to all of their Recurly sites (as they always have). Deep links to specific accounts, subscriptions, invoices or transactions still work because Recurly also supports an SSO login flow that originates at Recurly (known as "Service Provider initiated login").