Increase energy by supplying an additional fuel substrate that your body and brain can use immediately and readily. That in turn makes physical activity easier to endure, and mentally demanding activities easier to conquer.
There has been research pointing to the fact that supplementing with exogenous ketones could increase your metabolic efficiency. This would equate to better output and stamina while mitigating the requirements for ATP to working muscles.
There is also the benefit of exogenous ketones causing a satiating effect, making your hunger signal not as prominent. This will make harsh dieting phases much easier to tolerate and endure during times of famine.
As you can gather--all of these effects listed above won’t DIRECTLY initiate fat-loss or a leaning effect, but INDIRECTLY influence the possibility of fat-loss by giving you more energy than you would have had without exogenous ketones, in turn causing you to burn more overall calories.