Of course we make U Turns in practice, the question being why it isn't programmed to facilitate the same. It does have an adverse side effect insofar as it computes highly inaccurate ETAs which are transmitted to the client. As Korky previously noted, you could pull off a rank for a job only to find the client cancels before you get a chance to make a U Turn because he's told you're 14 minutes away when, in fact, once you make the U turn you are 2 minutes and 20 seconds away.