Bronze cleaning is much less expensive if carried out frequently. Regular visits mean less work is needed per visit and this means costs are kept to a minimum.
Bronze corrodes. It is very sensitive and reacts to pollutants in the air, liquids spilled upon it, guano and urine. When it does corrode, it usually looks unsightly. Bronze cleaning should prevent the need for costly restoration projects. Removing these sorts of contaminants often prevents the degradation of the protective coating and prevents the bronze from becoming etched and discoloured. Once the bronze has changed then only restoration can return it to what it should look like.
Regular cleaning is a protective process. It includes the reapplication of further layers of a protective coating such as wax. This barrier layer is the only protection the bronze has and so reinstating it regularly lowers the chance of the bronze becoming damaged.