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 two Potter rides (and those are the only Islands of Adventure rides reliably open during that time) 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.
That said, you should tour how you'd like: if you'd prefer to enjoy the atmosphere of Hogsmeade without it being as crowded, Early Park Admission can be a decent time for that. And if you want to get the Potter attractions out of the way so that you can finish your day at Islands of Adventure and move on to other things earlier, 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.