I've seen MCT oil is most commonly used in IF when you are doing daily fasts but not keto. In that case it's in bulletproof coffee attempting to give you a longer ketosis ride after your overnight fasting. Quality MCT oil with C8:C10 can generate ketones in 30 min to an hour after consumption and last for hours IIRC. So I've seen this considered a nice boost for folks doing IF but not actual keto diet.
MCT also has usefulness for people who benefit from having ketones in their system like folks with cognitive issues (Alzheimer's and dementia). It gives them a cognitive boost because the brain runs better on ketones than glucose.
https://www.youtube.com/watch?v=KGFUPSdATuw
I've seen Dr. Boz (Annette Bosworth) recommend it. But it's usually a temporary thing in that case which is meant to kickstart keto production more quickly. You still have to move to keto diet but the theory is that it makes it a bit easier or faster IIRC.
Most people are not well informed regarding MCT oils. In these videos, you can learn far more about them from a medical professional who uses Keto to help many patients with a myriad of health issues. If you are going to listen to random people on the internet, probably best to listen to ones who know the science behind it. Dr. Boz is one of the more highly informed on this matter.
https://www.youtube.com/watch?v=TmTfmqPd7o0