Eckhart Tolle has a really interesting perspective on thinking (thoughts). His perspective is that thoughts are a tool (a very useful tool, certainly, but a tool nonetheless). We either control the tool or it controls us. To bring about some measure of control to this tool, we need a way of turning it off (i.e., stop thinking). There is a simple way to achieve this: give attention to your breathing. It turns out that you can’t simultaneously attend to your breathing and think.
Perhaps constant, compulsive thinking brings on mental fatigue. By periodically stopping thinking, we can have more freshness in our thinking.