I thought it was something to do with triangle-stripping, but I might be wrong.
If I'm right, then it means having a row of quads all triangulated in the same direction, so their vertex winding order is always the same. I'm not sure how much of a benefit this is, I seem to remember reading some engines/platforms handle this much better than others.
Might be worth Googling up more info on "tri-stripping".
Here's a post from JamieF over on CGChat that might explain it better than I did:
StJoris is part-way there, UVs and Smoothing Groups affect tri-stripping, because if there is a UV seam over the middle of a consistent tri-strip, it will have to be split up anyway.
Eric Chadwick has a nice resource from a Game Developer article by Guillaume Provost concerning UV and smoothing breaks: http://www.ericchadwick.com/examples/provost/byf2.html