A long time ago I got a tiny little sketchbook as a gift. I have been using it now and then, but not very often. I did the colored doodle on the left using markers and colored pencils, mainly to try out color combinations of alcoholbased markers and colored pencils.
I have organized my colored pencils quite well and know which pencils I have; unfortunately I didn't know how many markers I have until the moment when I decided to get them organized. Now I am in the process of doing that. Knowing which colors I have definitely helps to keep me from buying the same colors a second time (something which happened in the past!).