Except for the very simplest cakes, it's rare to see one without icing. A good layer of icing protects the cake from drying out, and adds richness and moisture to each bite. Aside from those practical considerations, icing also provides a nearly limitless range of ways to lend visual appeal to your cake. Of course, your cake will only look perfect for as long as the icing does. If the icing should crack -- a frustratingly common occurrence -- even the best-decorated cake becomes a disappointment.
There is no single way to stop icing from cracking, because there are several common kinds of icing and thousands of individual recipes. The steps you take to minimize cracking will vary, depending on the type of icing you're using.