Received one today for a flight a week out. It lists my itinerary (outbound IAD-SEA on United), but leaves off the Air Canada segment connecting from Seattle to Vancouver. All ticketed (award) at the same time and (fortunately!) the ual.com itinerary and e-receipt still show the Air Canada leg. Imagine my momentary concern that that leg had been deleted. No text in the "preflight" to the gist of "here are your upcoming United segments, other connections may not be shown."

So, as others have pointed out, useless unless you want to buy one of the add-ons (though they seem to have gotten smart enough to not offer E+ upgrades when you are on an F ticket!) and in this case actually counterproductive because of the implication that the itinerary had been messed up.