True. I'm trying to check a sales director role. I'm confused how the Classification section in the emp record work with the roles' permissions and restrictions. Trying to restrict the role to a particular customer category.

you can restrict user by subsidiary or location. There is no way of restricting by customer category since customer category is part of the accounting list and does not have any permission criteria to set. There is another option though, by adding a custom segment for the entity(customer) and define ACL(Access Control Level) by role for the custom segment. This is a bit convoluted way but far more flexible and powerful. Note that suggestion is in theory haven't tested that.

@Sam-I-Am as far as I know you can restrict roles only via NetSuite vanila classification: Subsidiary, Class, Department & Location. You cannot restrict role base on a custom segment.

How about applying the segment to customer and use the segment's permission to define users role? It was a theoritical suggestion .

@Sam-I-Am I believe it can works, that's in case the use segment for this purpose only. Another way to consider can be to publish locked dashboard with relevant saved searches and/or use workflow action of return user error according to customer type & roles

Yes you are right, I haven't tested that but it should work because this of the permission schema.