You understand that petting the office cat is important but need to get everything else done, too? That's where utilization tracking kicks in. Firstly, you will have to set the days and hours the resource is available for work. Then Ganttic will calculate the utilization percentage using the tasks you have set for that resource for the time period you have selected on the timeline.
It's a great way to keep your employees from overworking by giving them just enough tasks. Since you can set utilization percentage to tasks, too, you can set tasks that take place simultaneously. You can choose how much attention each task needs and divide you resources' time accordingly. That way you can set a task named "Petting the cat" for Carl, and set the task utilization to 5% for a week, and hope for the best.