Difference between S4S Basic and Other License Options

S4S Basic is licensed against a domain name while other versions are against the Salesforce OrgId. 

S4S Basic looks at the host name on your Sitecore web server. The name is listed in the IIS Site Bindings page and is read by S4S at runtime. If a Host Name does not match a line item in the license file, a license failure message will be sent to the Sitecore log file (the logging level should be "DEBUG" to view the granular details). Note the following points about this form of licensing:

1. System administrators need to be aware of the link between the IIS Host Names and S4S licensing. A change can break S4S licensing.
2. Non-production servers, like DEV, TEST, and PREPROD, cannot access a Salesforce production instance as they will not have the IIS Host Names listed in the license. In an ideal world, this is not a problem as testers and developers should only be accessing Salesforce Sandboxes and Developer Editions from Sitecore non-production versions.

S4S Extended and other versions beyond S4S Basic do not query the Sitecore server so are more tolerant to change. The licensing keys for this type of license are the Salesforce organization ID and type. These are typically more static within an organization, although be aware that upgrading from Salesforce Enterprise to Unlimited will record new license keys.

Existing customers can upgrade to S4S Basic to Extended to take advantage of the more flexible licensing model.