What is the cost option in Exchange connectors?

What is the cost option in Exchange connectors? If you add a cost from 1 through 100 to any Exchange Server connector's Address Space tab, any messages that use that connector take the new cost into consideration when e-mail is routed. Routing cost typically ranges from 1 through 99. The default is 1. If the cost of a route is set to 1, other routes are used only if that route does not work. If the cost of a route is set to 100, that route is used only when all other routes does not work.