Some say that ketones are a more effective form of fuel for the brain. You can believe it or not. People on nutritional ketosis usually report being more energetic and having more mental clarity.
The fact that the body dont make ketones if glucose is abundant dont mean that glucose is a better fuel either.
Being a fat burner has some other benefits.
You dont have to worry about insulin spikes, sugar crashes, or something similar.
You are less dependant on the time and frequency of your meals. If you eat more carbs than needed, some of them are transformed into a less available chemical form (if you are geared to burn carbs). If you eat more fats than needed, they are just stored awaiting to be used.
If you decide to cut calories you dont put extra stress on the cells because they already are geared to metabolice fat. On a high carb diet you do.
Being honest, these are benefits of a low-carb fat-burning diet, not necessarily keto.
Surely making ketones put some extra stress on the liver. But on the other hand a glucose burning diet puts extra stress on the pancreas and nobody seem to care.
The tiredness and mental impairment that some relates to a keto diet is believed to be caused by a major lack of electrolites. High carb diets promotes liquid retention, low carb/keto ones dont. When one goes from a high carb diet to a keto diet a lot of liquid is lost, and this causes a massive electrolites and minerals loss. Taking extra supplementation during the adaptation phase seems to alleviate it.