It's not just about clean shoes ray, leather that isn't fed will dry and crack or stiffen, especially if it is rained on and then left to dry in centrally heated room. A good leather cleaner helps to keep the leather supple, a very expensive pair of shoes or a handbag, should be looked after with a regular application of leather feed, i do that with my radley bags, they even put a little bottle in it when u buy them.
Also, plastic shoes will last forever and need not be cleaned the same, they are also cheaper, leather costs more and will probably not last as long or wear as well, but it is better for your feet, more comfortable and keeps your feet cooler, they also tend to look good too. leather is a more expensive product but does not wear as well as plastic, but u have to pay for the quality and the comfort.