It doesn't matter. They are writing. Often, in this free writing time, the mind relaxes and ideas begin to form. Solutions to dilemmas present themselves. A scene that isn't quite working clicks with a new slant or idea for change.
Miracles do happen.
A few writers play hands of Free Cell, or hand Solitaire. There is something psychologically soothing in manipulating materials, like the alphabet blocks or shuffling a deck. Rearrange the furniture. Do something physical. Take a walk, get some air.