The control-logic of section access worked on fields which access might be per OMIT denied and/or that only certain records in regard to specified KEY values are available - and this is independent from any objects or sheets. A visibility-control of sheets/objects could be realized with section access but it's not really a security-measure else just some kind of usability.
I think this post will be quite helpful for you to understand what section access is and how it could be implemented: Section-Access.
