Right, so I explained that to my Ambassador when she was assigned to me. And what she does, for stays where the Your24 has been approved, is calls the hotel either the day before or the day of each reservation (or in the case when she's off both of those dates, then 2 days before, but that hasn't come up more than a couple times). And she confirms with someone that they are aware of my arrival time. This has helped avoid the awkward front desk issues and, purely my speculation, I think has also caused some upgrades and welcome amenities that I might not otherwise have gotten, purely because of the manual intervention. I routinely put in for Your24, even if it's just for a 1pm or 2pm check out--or, at a resort, for a 3pm or 4pm check in/check out time, in order to confirm the late check out in advance. (At normal properties, you can still get 4pm check out even with a Your24 check in time of 9am or later.)

YMMV, but this is the only thing I really ask my Ambassador for consistent help with, I value it highly (I do not like to risk that the room won't be ready yet, especially when I have my family with me), and it works. She has also helped arrange shipment of stuff (lost iPad, have clothes sent from one property to another and dry cleaned in advance, etc.), but only on rare occasion.