Big topic, this one. Basically those stats can reflect your current fitness state and, if used properly, could be useful in planning / tracking your workouts and training plan. There are whole books dedicated to this matter. For starters, this is probably a good short intro
I use these on a daily basis, after reading a couple of books on the matter and learning what these are all about and how they work. But I’m the opposite of your typical athlete who doesn’t want to bother too much with numbers, I’m a data nerd and have spent quite some time studying what these mean and how they can affect your training. At the end of the day I believe training is a mix of science and a bit of art too, since every athlete is different. I’ve found these to be a good guideline, and I like to see my PMC (Performance Management Chart) in TrainingPeaks or other software (*). I have found the numbers to be quite interesting and telling (for me), and once you start using a power meter on the bike I think they become even more valuable. At the same time sometimes you see weird things that don’t have a direct explanation, and there is no substitute for how training feels (i.e. your TSS for a workout can be low, but you can still feel like crap after doing it!).
At the end of the day I don’t think you need these at all, but it’s an interesting tool if you put in some time.
(*) I’m a software engineer, so naturally attracted to this sort of stuff. I use Golden Cheetah, an open source desktop tool that is not easy to use but that is super powerful (it predicted my bike FTP to within 1 Watt of real test)
Hope that helps and sorry if this got too long, but this is one of my favorite topics 🙂