Memorize is good when you use a custom morphed character. Say you tweaked lovingly each of the N dials to create THE perfect girl/boy/horse/cube/whatever. You have added him/her/it in you new scene, added some clothes/accessories that you had to tweak to match the proportions. Now you apply a pose that you got in the freestuff and that was saved with morphs : your character gets deformed and you'll have to reload it from the library and re-tweak all the clothes/accessories unless either a) you have made a MOR pose for your character, or b) you have memorized him/her/it (in the latter case, the posing will be lost, but the morphs will return to their original state).