We used to use sections for establishing user access rights by using section limitations on the roles. However, lately, we have found it easier to use a subtree limitation based on content for this purpose, rather than sections which require an extra step for the same outcome.
The uses of sections that I think still stands out is the ability to create overrides based on sections, and the ability to assign the same section to multiple content trees.
That being said, we don't use sections in most of our sites. On one that we used them on, we created a section that is only visible to logged in editors, allowing entire sub-sections of the site to be created offline, invisible to anonymous and guest users. Once the section was done, we switched the section to the standard section to make the new section visible to all users.