People have gotten into trouble -- legal, political, or otherwise -- because
they emailed documents that contained secret or libelous text that they
didn't realize was still there. Some of that was in so-called metadata, and
some was in markup that happened to be hidden. (For background, see
http://www.msdn.microsoft.com/library/en-us/odc_wd2003_ta/html/odc_WDProtectWord2003.asp
and
http://support.microsoft.com/?kbid=834427.)
To try to make you aware of what's in the document before you "publish" it,
Microsoft added the feature that automatically displays markup when you open
or save. If you choose not to take advantage of that reminder, you can shut
it off -- but then don't complain if your boss receives your letter that
still contains the deleted phrase "Dear Pointy-Haired Boss, take this job
and..." ;-)