Your decision totally. I think my personality is one who really likes to do a lot of up front planning, so that means a touring plan is something I love putting together. My son, 22, is the same way, so I have a blast working together with him and planning any WDW park day.
Despite my next trip to Orlando (March of 2019) being number 35 for me and despite my only going to one WDW park (the Magic Kingdom) for one day on that trip (coming to Orlando for a family wedding and family activities -- only planning two theme parks days -- the MK and SeaWorld, our two favorites), what am I doing? -- planning our MK day with the touring plans app. Two of us will be doing the Keys to the Kingdom tour and then some attractions after that and two will be doing a busy full day at the MK. The plans give me a good idea of what we can fit in and is a great tools for planning our day, setting priorities. When lines are longer than the original predictions, we sometimes decide to skip some things, etc, and can re-optimize during the day. One day for one person at the Magic Kingdom at the value time is $116 when you includes taxes, and the Keys to the Kingdom tour for two of us is another $99 pp, so a good tool to help me make the most of that very expensive day, especially for the price they charge is worth it to me.
I like it that they keep up with park hours, extra magic hours, special things going on, parties, spring breaks across the nation that might affect crowds. I like their ratings by age group for attractions if it's something we are maybe considering adding that's new.
I'm a bean counter personality that usually doesn't go for the extras (I don't pay for a credit score, find out about my ancestry, check the kind of mix my dog is, buy a magic band when my little plastic card is free, etc.), but I do pay to look at the touring plan recommendations and wait times.
I've been using the touring plans from the book (before they had the computer version) since 1981. They just with their computer models help me make better decisions. It's not perfect, though. If crowds are higher than expected and some lines are longer than expected, we though know where we are on our plan and often reprioritize and drop attractions we don't care as much about.
I've just had way more fun on days that I have used their plans vs. days that I have done my own thing, especially at busy times which now at the MK seems to be all the time lol. And with having done more up front planning, it makes it easy at the park to just really enjoy ourselves and the wonderful vibe at that very happy place, that is a little happier if you can do fewer really long lines.