Are unsaturated fats beneficial?
I don't know that unsaturated fats are necessarily good. That is one of the few differences I have with people like Walt Willett at the Harvard School of Public Health. They say it does not matter how much fat you eat as long as it is unsaturated -- but it does.
First of all, fat is very dense in calories, and it doesn't matter whether it is unsaturated, monounsaturated, or saturated. Fat has 9 calories per gram, protein and carbohydrates have only 4 calories per gram, so when you eat less fat you are going to consume fewer calories without having to eat less food.
Are any fats good for you?
The truly good fats are not so much the unsaturated fats as the omega-3 fatty acids you find in fish oil and salmon and in some plant-based foods like flax. Part of the problem when you eat unsaturated fat is that much of the unsaturated fat people consume is rich in the omega-6 fatty acids, which promote inflammation and autoimmune responses. The truly good fats are not so much unsaturated fats as omega-3 fats.
And you don't need that much of it. You can take 3 or 4 grams a day of fish oil and that is really what most people need. And you can also buy the fish oil that has all the bad stuff in fish removed -- the omega-6, the PCBs, the dioxins, and the mercury. Then you get all the benefits of eating the fatty fish but without the extra toxicities that are found in most fish these days.