This flag should be checked for articles that have unnecessary content (for example, discussion or rambling exposition) that should be cleaned up and removed. You should also mark the specific content that has the cleanup problems using the associated Editorial block.
Manual of Style
TODO: Figure out which piece of Manual of Style this relates to
Once the entirety of the article has no extra content you may remove this flag.
Be sure to mark which content has problems using the associated editorial block: Template:Editorial/Content_Cleanup.
The editorial block should be as close to the content with problems as possible. If that’s not possible (for example because the problem pieces are in a rigidly-structured part of the page), then put it in the Editorial Block at the top of the page.
If most of the content has problems, the editorial block should go in the Editorial Blocks section at the top of the page.