The other side of the coin. A case to be made for not training with any of this.
I am an engineer by education with a heavy science background. I love the numbers. I love trying to figure out the correlation between how intense a workout is to my relative fitness and how they tie into my goals. However I try very hard to not let the data get in the way of the enjoyment of the sport. I have mentioned Rick Mann, multiple Kona qualifier and sub 10 hour Kona finisher. He has qualified for the 1/2IM Championship this year and will do excpetional. As an age grouper (Tri speak for non professional) with a family, full time job, and other life demands he is one of the best if not the best in the St. Louis area at long distance triathlon. The kicker, he doesn't use any of this stuff. That is a pretty strong argument for not using it (or a strong argument for hard work and great genes!).
He is PASSIONATE about IM. He is experienced in IM and has a natural gift that he has worked very very hard to tune. He has been doing long distance tris since the mid to early 90's so he has been able to figure out by "feel" and experience what works for him. He has had a lot of great races and I am going to guess he has probalby had some that he would love to do over again but regardless he has two things that I don't. 1 - Natural ability 2 - a lot of experience
When I started, my goal wasn't to do the Ironman 10 years from then, it was to do it in 2 years so time was not on my side and my tolerence for trial and error was/is pretty low. To address the second point, I may have some latent, natural ability but I needed to get the most from what little ability I had as fast as possible. Lastly, Rick and many others just go hit it and seem to be so in tune they know when to push and know when to pull back. I don't have the frame of reference yet to know when that is which can quickly lead to "blowing up" on race day. The data helps give me that frame of reference.
Lastly, and at the risk of getting mushy, let me warn you to not let the data get in the way of enjoyng the sport. If you pursue this stuff, take the time to enjoy the sunrise / sunset. Stap on your shoes and tear out on a trail run for the fun of it. Go ride you bike with your kids / wife / whatever. Do a 5K with your daughter or son. All of this stuff is just a means to an end with the end being health and quality of life. It is easy to get caught up in the goals and the goal are a great catalyst to kick start your fitness but the secondary benefits far outweigh the primary in the grand scheme. For me, Rene is now my trathlete wife (who is better than me), my kids did their first Tris last year unsolicited by us. We did a 5k as a family a few weeks back. NBB and KGB swim now and want to learn to lap swim. NBB walks at recess and walked more miles than any other kid in his school last year because he wanted to. KGB periodically wants to go for a run with dad (she is 9). It is just a world that didn't exist prior to us getting into this sport and has happened just because. Kids emulate their parents and as a wise father once told me, they are watching and learning even when you are not actively parenting and that is when they really learn from you.
So just to summarize, the data is like anything else, it is a tool. Don't get so focused on the tool that it gets in the way of the project. If you are looking to kick start a program, pick a 5K or some other event sometime in the future, register for it, put it in your calendar, and tell your family and friends your goal. You will be amazed at how spending your money and committing to a race will motivate you. It has for Rene and I (and several others) and my family and I are better for it.
All for now,