Why have zoning?

An email just popped up asking me why we have zoning. This is part of a long debate about land use planning and I have not the time to write it out here. In contemporary Irish Development Plans the reason for zoning is to indicate to property owners and to the general public the types of development which the Council consider most appropriate in each zone. Sounds simple? Well in principle it is! But this hides a debate currently raging about how zoning of land is carried out, who benefits, should Councils buy up land before re-zoning, etc. Zoning is perhaps the most controversial part of Irish planning.