Perfect for tucking in your pocket or purse, so thin and flexible, but strong--they hold up well. Sort of a versatile "diary" to record random information. I like the plain (no lines) so I can draw a diagram or write small or large or whatever. Since this slips so easily into almost anything I carry, I always have something permanent to make a note in, which is easily retrieved later. And the pocket on the back inside cover can hold business cards, stamps, etc..
Also, for an organizational system, I bought several packs of these in different colors to record information for reference. I label these "Health" (enter symptoms, visits, tests, etc. with dates), "Guests" (include dates and menus), "Weight" (if I'm keeping track!),"Auto" (what and when repairs were done), "Computer" (problems to have my kid teach me how to deal with when he visits!), etc.--you get the idea. This works better for me than most files and other systems I've tried! Probably because they're accessible--they can be tucked into a small convenient space, and are good-looking enough to mingle with the décor.