HRV is an area where I do not feel very knowledgeable despite using it. I can't explain it like cfboy can. Alan Couzens has a series of blog posts about HRV that might be helpful, they were for me (today).
I use an amalgamation of my training load (CTL and TSB), how I feel, how I slept, mood, HRV, and the nature of recent rides to determine my workout type and duration. I am very careful about when I do a HIIT session. Not so careful about a zone 2 ride. I have had several long rides in the past month (400km and 600km) and therefore no structured HIIT for almost a month. I had food poisoning that took over a week to resolve, yes, it was obvious on the HRV. So, I was started to feel ready for a hard workout but the HRV data was not flashing a green flag but not signalling red. On 5 hill climbs I did 5 PBs. So, HrV is just one piece of information. Flash forward two days and my LF/HR ration is terrible and I slept poorly. I did a good solid 2-3 hour zone 2 ride in 90+ heat with humidity. Next day. I went on a zone 2 ride and I barely could ride. Looking at my HrV data retrospectively, I should have taken a day off but I felt good at the kitchen table. My LF/HF ratio is coming down but I decide to take a day off today. I have ridden 10/12 days including a 600k and one pretty hard hill workout where I hit new PB for two short power durations. (1 minute and 3 minutes).
My reasoning for using HRV is to try to predict if I will get a training response to a hard anaerobic workout and/or whether it will detrimental because even though I am only in the 64th year and still feel young, I know I can only get stronger during recovery but more importantly, time off the bike due to overreaching is very detrimental. So, if I need a rest....it only means I will come back stronger after it. OTOH, if I overdo it, it might take several days or more to recover. I never want two zeros in a row.
https://www.alancouzens.com/blog/overtraining_HRV4.html