Most structured data is relational. If you include data like (someone else's) web site content, images, sound files, video files, etc, it's a different picture (pardon the pun).
It's a bit weird, but logstash & elasticsearch (and relating/extracting data when and where I need it into postgres) have made my life so much easier
1. Single entry point.
2. Not having to share your filesystem.
3. Centralized security separated from your OS
4. Simple key/value access (no folder structure)
5. Abstraction of the filesystem (like #2)
6. Distribution of data over multiple nodes.
7. Separation of NoSQL admin and network admins.
8. Shiney new thing :)
Some databases also let you define secondary indexes.