This feature is only for new 4.x templates.
This is a 3.x feature we have brought into 4.x
Go to: Design>>Desktop>>Site Design
Under Sidebars are options in a drop to show and hide the right and left sidebars
Hiding the sidebars on the homepage will allow the homepage to act as more of a splash page.
Hiding the sidebars except on the homepage will allow for more room in sections, articles and modules.
Hiding sidebars in articles
Go to: Content>>Create a new article
or >>Active Articles 
Edit
Scroll to: Toggles and Keywords
Check Hide Sidebars on Article?
