SEO HTML is easier to update
SEO makes updating content at a later date easier. SEO generally creates cleaner HTML which means updating that content can be done easier by web developers and also employees.
One of the biggest problems that can occur from messy HTML is that when it is loaded into a content management system, a lot of the styles are hidden from the user who is updating that content. If the user edits the content without interfering with the underlying HTML then everything will be ok. But for example if a user deletes some text, then inserts some new text, the HTML code that was present will be missing which can effect the visual style on the page.
Search engine optimised text doesn't include superfluous tags and relies on semantically correct tags decreasing any side effects later on. CSS should be applied to text based on their tag names and not class names, this allows users to update content without any side effects as all tags have been set with CSS.
Correct use of search engine optimised HTML is very important for your ranking in google and other search engines. We have found clients who are given poor content to update in the first place can destroy the previous poor optimisation efforts to a point where the text is not optimised at all. This is quite a worry and means that it is even more important to create cleaner HTML through SEO.