Here is an interesting article written in Discover about research showing that hobbies have positive psychological effects on people. People doing their hobbies tend to enter a state of mindfulness while doing them. This provides a temporary escape from stressful thoughts and allows the hobbyist get some mental rest. When a hobbyist finishes her hobby activity she tends to feel rested at the conclusion. This is definitely the case for me when I finish reading, or painiting, or playing tabletop games.
Discover Magazine: The Psychological Benefits of Picking up a Hobby