Fasting promotes autophagy and improves insulin resistance, if you do actual fasting (no calories during fasting). Many people have what's called "metabolic syndrome" which is low insulin sensitivity (high insulin resistance) and that causes many problems eventually leading to Type 2 diabetes.
Fasting with small "breaks" (100-200cal snacks) breaks a true fast (>50cal) but still results in overall reduced calories, and is more sustainable for many (or a path towards true fasting).
You lose weight in fasting due to reduced calories. How you do it determines the benefits - merely reduced calories, or more. Some people have very little weight loss with reduced calories diets b/c their metabolism (insulin sensitivity) is really messed up and won't see benefit until they do true fasting.
I like OMAD (one meal a day) as it feels the "easiest", though I have done regular multi-day fasts in the past and the hardest part is figuring out what to do with yourself since you're not spending time cooking/eating.
A good book is The Obesity Code[1], with lots of background and fasting schedules.
Really, the most benefit I've had from fasting is resetting my appetite - I am now satiated and full from a "normal" meal, and thus eating a reasonable amount of food. I used to easily be able to eat a large pizza and then a pint of ice cream every night (obv that leads straight to obesity). Now 3-4 slices of pizze + side salad is more than enough to fill me up and I have some pieces of chocolate for dessert.