I've been using the plan for every trip since 1991 and am a big fan. If it's a moderate to light crowd day, I'll deviate. On heavy crowd days, I really like to stick to the plan. Do note that we have been to the park so many times that we typically only have about 12 things on our plan, and after that we shop, do repeats, try new things, etc. so usually are looking at line and FP+ availability. It's a great way, though, to get your core stuff in efficiently.
Before FP+ I loved it that the plans told you when to get fast passes and when to use them. With FP plus I love it that the plans work around your fastpasses and sometimes even tell you not to bother with what you have and to maybe get something else, as what you got isn't going to be helpful in saving overall wait time. DS 21 and I do the planning together, and it's a ton of fun. I also use these to decide if I even want to go. I do this before I book any air or lodging and sometimes based on long stand by wait time, I have decided not to go to Disney.