When you click "Optimize," our software arranges a plan that minimizes aggregate wait times over the course of the day. To a lesser extent, it also minimizes walking times.
Our software may calculate that there's no benefit (in terms of saving time spent waiting and walking) in using Early Park Admission, especially if you are using Universal Express to reduce your waits. Basically, it's more efficient for you to experience the 2-3 rides that are open during Early Park Admission later in the day using Universal Express than it would be to walk to the back of the park and do them during Early Park Admission, when everyone else in the park is queuing up for those same 2-3 rides.
That said, you should tour how you'd like: if you'd prefer to enjoy the atmosphere of Hogsmeade, Diagon Alley, or some other part of the park without as many people around, Early Park Admission can be a good time for that. And if you want to get the open attractions out of the way so that you can move on to another park or lounge by the pool, by all means use it. These are not bad options, even if our software calculates they're not "optimal." Although we love them, optimal plans may not maximize your happiness, and that's okay--do what makes you happy!