I've been developing my own bootstrap theme for odoo v9.  I ran into an issue where I had added all of my theme snippets as structure, since the theme tutorial doesn't really explain the differences.  After many hours of creating a website, getting the front page looking like I wanted, I went to edit a secondary page.  unfortunately the front page structure followed to my secondary page, because I had used the structure subsection.  After more troubleshooting, I discovered that structure seems to edit website.layout, and follow you to subsequent pages.  I should have used feature as my category.  feature snippets only stay on the page you are editing. Perhaps someone could fully document this?