...
The Security Connector for Leads is only required if you want visitors to log into the Sitecore website using credentials stored in a Salesforce lead record. The Security Connector overrides the ASP.NET membership provider so user data is stored in Salesforce but appears in Sitecore under the “salesforce” domain name. After installing this option it is possible to control the visitors Sitecore role, user profile, landing page and more, directly from Salesforce.
...