Hmmm....I still don’t see any advantage of doing this. The [*content*] is basically a TV itself. So, if you want a header or sidebar, just create other TVs for them...they will all appear when you edit the page. And, if those header and sidebar TVs are of rich text editor type, the editor will not be able to differentiate them from the [*content*] except for the description you provide for the TVs.
The thing with modx is flexibility...if you want you sidebar to be another page, that’s fine...you can use a snippet like GetField to pull in the contents of a another page into your sidebar/header. If you want sidbar/header in a chunk, fine, if you want your sidebar in a TV, that’s also fine, if you want to include the contents of an external file as your sidebar, that’s also fine.....I could go on and on...
Think of it this way: if the content will not be changing and will be same across the pages - throw them in a chunk. The advantage is edit once deploy many times. If on the other hand the content of say your sidebar will be changing based on the page, put them in a TV (or pull them from another page if you wish). Heck, you can even have TV-based chunks in modx.
cheers/k