Q: What is a Content Library?
Content library is your place to store and organize content for re-use/ repurpose. It is not only about reusing sections. You can manage sections in the library, the images, videos uploaded by you, fees items saved in the library. You can add/ update/delete these elements in content library.
Q: You mentioned about Content Library. How is it different than Section Library?
Section library is part of content library. Content library allows you to manage following content
3. Fees (available for Team+ plan)
Section library can be imported to proposal and template, similarly the fees items can be added to fees table in a proposal or template; image uploaded by you can be reused in proposals/templates, so are videos.
Refer to their respective guide for more details.
3. Fees Library (available for Team+ plan)
4. Video Library