I was tired of writing little notes and measurements on my hand, writing shopping lists on whatever scrap of wood was laying around the job site, and trying to draw plans on napkins.  I needed something I could carry with me all the time.  Too large and I'd leave it in the truck.  Too small and I'd lose it in the laundry.  This is the perfect size for my back left pocket.  An added bonus is that it balances out my wallet and makes driving a lot more comfortable.  Within 2 days I carrying this in my pocket I stopped noticing that it was there.  Within a week I was filling up pages with everything from coworkers' lunch orders, to email addresses, lists of specialty tools needed for jobs the next day, small sketches and diagrams, and whatever else I wanted to remember.  I'm one of the last people that will eventually start using a smart phone, and this greatly helps delay the inevitable.