It will be interesting to see what the Yield's all about--once it's finally used. It was discussed quite a bit during the preseason, so someone must use it sometime. Otherwise, it'll be much ado about nothing (and might wind up that way anyway).
A major reason not to use it is that it would make the team being yielded pretty mad. If you're trying to build good will, you might tend to avoid it--unless you're sure the team you yield would be eliminated. Of course, if teams are mad at each other already, it wouldn't make much difference. Since Charla and Mirna are gone, and Chip and Kami are reconciled, there doesn't seem to be any animosity among the teams left.
Another thing is the timing. You can't use the yield just any time. If that were the case, it would be very handy, for example, to make another team miss a plane or ferry. But they occur at certain places in each leg.
We've only seen the yield twice:
-During episode 1 Alison and Donny found the Yield during the beef carry. The five teams on the last ferry were probably pretty close by the time they reached it. They didn't know what else they had to do and how long it would take (they still had the detour at the blue hotel).
-We also saw it on the Aurora in St. Petersburg. They had just arrived and had both the detour and roadblock to do. (Besides, Bob and Joyce were well behind and their elimination was pretty likely at that point.)
In each of these cases, the Yield occurred early enough that there was plenty of race left in the leg. Using it wouldn't assure a team's elimination and might make an enemy. It would be hard to decide whether to use if since they don't know what's coming up next.
I also don't remember seeing how long the wait is. It's possible each Yield is a different time. Perhaps the times aren't long enough to make that big a difference.