I've been using the Windows version of Scrivener since 2014.
I think my way through a story by writing about it, so in addition to the manuscript itself I end up with lots of notes, ideas, research, character sketches, scene sketches, drafts, etc.
Scrivener allows me to keep all of that project-related crap in one place, along with the manuscript. Much better for me than working in both Word and OneNote, which was how I used to do it. It's really a writing project management tool.
A key feature, called Scrivenings, allows you to write your manuscript in as many sub-documents as you want--I typically write each scene in its own doc--but read and edit the manuscript as if it were all in one document.
Another thing you can do is rearrange the sequence of scenes without impacting the manuscript, to see how it reads without actually making the change. You can also label the scenes and then arrange them by label. For instance, I have a multiple POV novel, and I can have Scrivener pull the scenes for a single POV into one doc, so I can check for voice and story continuity, again without impacting the manuscript.
You can also view scenes in corkboard or outliner formats if you like.
Last year I purchased the iOS version, so now I can access my Scrivnener projects anywhere, from my iPad or iPhone. Paired with a bluetooth keyboard, the iPad becomes a bona fide writing tool, and I was surprised how productive I could be while writing on the iPhone 5s, despite it's small screen.