There is no denying that growing an anal sphincter in a petri dish is hilarious. There is also no denying that nobody reading this would enjoy being without an anal sphincter, so it's good that there are back-ups being developed.
There are three main features that everyone needs in their various sphincters. The first is completeness. Although the muscles in sphincters are fairly strong (certainly enough for their respective functions), and the nerves sensitive to impulses, none of the necessary functions can be performed if the loop of the sphincter is broken. The second important feature is muscle tone. Through repeated use, and complications from aging, the muscles can stretch. These first two features can be repaired through surgery.
The last feature difficult to fix. Possibly the most important feature of a sphincter is the same as the most important feature of a race car: responsiveness. Sure, power and good design are necessary for real success, but it's all wasted if the damn thing won't do what it's told. It's this last problem that a petri dish grown sphincter can solve. (So far, there has been no luck creating a petri-dish-grown race car.) These new sphincters were started by placing human muscles cells and mouse nerve cells in a circular mold. With the right care and feeding, the cells grew and expanded to make actual sphincters. The sphincters were then implanted in mice, and because of their nerve cells, could connect to the animals' nervous systems and function much the way mice's original sphincters did.
This level of functionality is something that hadn't yet been managed. If progress continues, it means that a patient might have a new sphincter grown from their own cells, and have it placed in their body through surgery. In all seriousness, this will improve the lives of a lot of people.
Image Credit: Wake Forest Institute of Regenerative Medicine