Premium tokens allow you to do more when you are not online. You can queue up multiple researches as well as multiple buildings to be built in your villages, as well as move buildings in your villages. Along with a host of other features such as the village overview screen, auto scouting and more. It's a bit like having your own personal assistant working for you while you are not logged in!
Please note that the offline features do not operate continuously, they will activate once every 2-6 hours while you are offline. If there are no resources to scout in your parish, or no goods to be sold from your village the automatic feature will not activate.