Leather takes care of itself, just like skin. This is accomplished by means of fats. With wax or balm you can aid this natural process. The wax is being absorbed by the pores, it gives the leather a deep shine and restores it, as a result of which the leather keeps its good quality for a longer period of time. Wax makes sure that the leather stays water resistant. It is important to frequently repeat the process of waxing or balming.
In general it is best to maintain the leather once in six months, but this of course depends on how much an item is used. Too much maintenance makes the leather thinner and therefore weaker. Because wax and balm remain in the pores, it will take a while before the leather is insufficiently greasy again. However, it could be necessary to treat shoes more often, because they get dirty faster.