I've been working on a child theme of twenty twelve.
I want to have sidebars on SOME of my pages (turns out, they are "pages"), and twenty twelve gives me very convenient options for layout on a per page basis.
I want some OTHER pages to be full width, no sidebars. Sadly, these are NOT "pages"--I want this for my single post pages and for my category archives. The category archives are most of what is listed in the top level menus, and a primary piece of presentation and navigation.
It is very easy to remove the get_sidebar() line from category.php (yes, I am working on the child theme). BUT the page content stays huddled over on the left-hand two-thirds of the page--NOT what I was after. (The custom post formats do not affect the width here at all.)
Yes, I can remove all widgets from the sidebar and then ALL pages turn out single-column, but I actually WANT a side bar on certain pages (that are "pages").
I can usually bumble around with the php and do what I need, but I am stumped, not even sure where the width of the sidebar-less category pages is being controlled.