This topic came up recently among the Word MVPs, and Cindy Meister posted
this explanation:
Early in Word 10 we added a mini-feature -- having table autofit in pageview
keep tables inside the page margins. The original motivation for this was
printing web pages from Word, though it's useful more generally. Once we
added table autofit, then a table will expand horizontally for the longest
word or widest picture in each cell -- even if it means that the table
expands right off the page. Instead we had table autofit in page view try
to keep the table inside the margins. Of course it still needed to be
possible for users who wanted to have their tables extend into the margin to
do so. So we don't keep the table inside the margin if the user explicitly
pulls the table edge out there (which causes the table to have a table width
wider than the margin). The change did not affect Word 97 (and older) docs
since their tables have "resize to contents" turned off.
Since we didn't want to change the layout of existing Word 2000 docs, we
used a compatibility option.
For "Use Word 2002 Table Style Rules"
This setting involves some rather subtle changes to conditional table
formatting. You can see a difference if you follow these steps:
1. turn setting on
2. new document
3. Table / Autoformat and choose "Table 3D effects 3"
4. choose apply
Repeat steps with setting turned off, in a new document.
The idea behind these options is that we have taken a few bug fixes in
these areas that may cause a document to look differently or lay out
differently. When we make changes like that, we use compatibility
options so that older documents look the same in 11 as they did in the older
versions.
If you have the settings turned off and you save, in an earlier version
of Word, you may see the document layout slightly differently
