D365 Licensing vs Security Roles – Why can users access data without the required license?

I am working as a Power Apps developer in a Dynamics 365 environment that has the Field Service module enabled. In the same environment, some users only have Sales licenses.

I assigned a security role that provides read access to the Warehouse table to a user with a Sales license. The user is able to access and read the data successfully, even though they do not have a Field Service license.

This makes me unclear about how licensing is enforced in Dynamics 365. If security roles alone can grant access to tables, how do licenses actually restrict functionality? Why is it necessary to purchase additional licenses if users can still access data through security roles?

Could someone clarify how licensing enforcement works in this scenario and what the best practice is?