Market share
Increasing market share is one of the most important objectives in business. The main advantage of using market share is that it removes the effects of industry-wide macroenvironmental variables such as the state of the economy, or changes in tax policy. For example, if you were one of only two psychiatrists in Chicago, then it would not matter how bad the economy was because you would always have a huge slice of the consumer-base "pie" for your service. If your service was less needed, then advertising more would help increase your market share.