Our minds are always busy. During the day we process and comment all kinds of impressions; we constantly think or plan. At night we're doing the same thing in our dreams. Poor mind, always at work...
That's why it feels so good to turn off the input. You don't even have to meditate, just concentrate on what you are doing Right Now, without any speech balloon. It's such a relief to relax from inside.
Finally the mind quiets down, and can get some rest.
The effect is amazingly refreshing.