Last week I did a Storyboarding session with a group of people. It was a pretty complex communication puzzle that needed to be solved. 
There is a lot of information being processed in these three hours. But although it does require focus, I don’t think it is particularly exhausting. 

There are several reasons for that. 
1. I don’t have to keep the information in my head. It is all on paper, at the right place, and I can re-visit it when I need to. 

2. drawing is fun and activates a different part of the brain than thinking (I think)

3. It is easy for everybody on the call to follow “where we are” in the process. 

I can only recommend using your pencil when thinking – alone, or with others!