Yes, with a caveat. The app does a good job of optimizing and planning based on the ridiculous amounts of data from everyone. It predicts, based on the past, what time FP will be available if you get them at a certain time. Since it is just an average, there is always room for error, but the times are usually close to what they say.
An example: to get a FP at rope drop for Radiator Springs, the app will ALWAYS say it takes 20 minutes. I have never had this experience. I think this is a holdover from when they first came out. That means that if I go straight to get that FP, the time that was predicted is usually not the time that I get. This is where your flexibility is key; you have to be ready to go a little off plan as needed to make it all work. Take some time as you plan to decide what your priorities are–do you need to have every minute planned out? Is it more about the experience of being in the parks? Are there things that are “must dos” on your list, and the rest will just be as you go? Knowing before you get to the park how you will handle the changes that WILL happen to your plan makes the stress a lot less, in my opinion.
Long answer, sorry. Bottom line–the app is invaluable. Even better is using the app in park to adjust as you go. Have fun!