Positions are available for select pages and blog areas of your website, so not all sidebar positions are available everywhere. For example, on this page you cannot see the Blog Banner or the Post Inset sidebars because they are only available for the blog, archives, and full post views. However, you still get a lot of layout options with 22 positions and several sidebar groups that sit side-by-side will have dynamic widths. This means you can have up to four(4) widgets in a single row, but when you publish 1, 2, or 3, they will self-adjust in width to fill the space the fourth one would normally take up.
The left and right sidebar positions are separated for pages and the blog archives. This was done so that you can manage your widgets much better when it relates to the blog or to static pages that are not connected to the blog.