Knowing more about horses gives you more information to work with. Maybe they're nervous about something outside the arena.
Instead of immediately thinking, "What am I supposed to do?" you can start thinking, "What does my horse need from me right now?"
Every horse is different, and even the same horse can feel different from one day to the next. Sometimes you need to slow down, be clearer, or try something another way.
Being able to stop, assess the situation, and adjust your approach is a huge part of becoming a confident, thoughtful rider!