Confusing about Microsoft CRM licensing

Hi experts,

I am confused that how the Microsoft licensing works in terms of access to the different modules/entities in Dynamics CRM? My client is using two type of licenses which are:

1. Dynamics 365 for Sales and Customer Service, Enterprise Edition
2. Dynamics 365 for Sales Enterprise

My assumption was that the users having “Sales license only” will have no access to the Case entity but as per my observation both the licenses work in the same way. With proper security roles both can access Accounts, Contacts, Leads, Opportunities and Cases. Is this how it should work? If yes, then what’s the difference?

Regards