Unless you have a photographic memory (no pun intended) and can remember every option and setting on the complicated D300, a small "cheat sheet" is an absolute necessity when traveling. It has saved me from some stupid mistakes (wrong focus or metering settings), and most of all it provides a quick reference when you want to utilize one of the more esoteric functions of the camera.  If you can remember all the options more power to you; for me, the small price (and small size) of this reference guide is invaluable. It beats ending up with lousy photos.