The main goal is to depart trains thus making money.
While a routed train can always be departed it is important to keep an eye on marketing campaigns as well as the route subsidy.
Subsidy is a goverment payed percentage that will be added to each passenger onboard. The higher the subsidy, the higher the ticket income. To make sure you utilize the subsidy, a Lobbying campaign must be preset.

If too much time passes between each train departure, you will risk delays, which in turn will cause less passengers onboard your trains.