Are exogenous ketones for when you're fasting/doing a keto diet or for when you're not?
It depends. I experiment a lot. I've been fully Keto for almost eight years and I do intermittent and extended fasting. In fact, I'm on day seven of a salt and water fast only. I feel great. The first two days were the most difficult. I have three young kids, we are all active and I had a crash. My husband is a physician and worked with an engineer to have ketones made for me specially for marathon training while I was fasting. Our friends enjoyed them so he had big batches made and sells them. I make it a habit not to consume them but I was desperate. For the first three days of my fast, I used a scoop of exogenous ketones. They did help me get through. Now I am off of them until my next fast or long run (over 6 miles).
They can help with Keto, but they should not be used everyday for the long term. They become useless if you use them all of the time unless you are constantly intermittent fasting while working out.