What problem does this address?

Sites that don't have a centered column with the post content have trouble with alignments. An example of this is Stewart, where the single template uses columns to achieve a sidebar and places the post content inside the right column. This invalidates alignments but the user can still set them up in the editor, which is confusing.

Frontend:

Editor:

What is your proposed solution?

This is a tricky problem to solve. The first idea that came to mind is having the possibility to disable alignments directly on the post content block, since we do want them for the templates, just not for the content of the single template. Maybe the post-content block on the page.html template can be the same layout and we do want alignments to show up for that one.