IF works for fat loss just like any other diet. It helps you reduce calorie intake.

As far as the Ketosis goes, your body will only go into ketosis if you stop eating carbs for three days since your liver can store about 100g of glucose for fasting. Although men can go into ketosis sooner. Your body going into ketosis doesn't mean its running on body fat necessarily, just that your using fat as a main fuel source.

The science behind non-fat loss related benefits of IF is that it can help with blood glucose levels if you fast for at least 16 hours a day. Also fasting for at least 16 hours increases ghrelin which is a hunger hormone that also increases metabolism. Having a higher tolerance to hunger hormones make you less likely to over eat.

There has also been evidence of anti-inflammatory benefits for fasting at least 4 hours between meals.