I use notebooks in three sizes.  I like the smallest notebook for carrying in my back pocket.  This notebook is handy to have in your back, as it is too large for most pockets, but it bends really well and writes well.  The cover and binding will stay intact for a long, long time making them great for recording thoughts and ideas that you may not get back to for years.  I generally record product ideas and meeting notes in these and in a cramped setting they shine the most.