I think finding spells not on my bars is part of LearningAid's purpose. When you learn a new spell, they don't get added to your bars automatically after a certain point. If you level up in the middle of a string of fights or an escort quest, for example, you may forget to put that spell on your bar. Instead of looking back through your chat frame to remember what it was, finding the spell in the spellbook and pulling it out, LA can just tell you what you're missing and give it to you in its window. It is also useful when switching between specs (or learning a new spec).