Looking at fats as good and bad is very simplistic. Fats are very beneficial, especially saturated fats. There are certain times to eat certain foods that will really help you. Look at the different hormones that are at work and try to use them to your advantage. If you have just participated in strenuous exercise you need to raise your insulin level so your body can repair any damage that has just occurred and preserve muscle mass so it is not used to replenish glycogen. In this case you would avoid fat because it would slow the absorption of glucose, thus slowing down the repair process. You may want to eat something that will shoot your blood sugar through the roof like a baked potato. To enhance the efficacy of this process take in some lean protein, or fast digesting protein, like whey.
When you are realtivly inactive you may want to have fewer carbs. Try eating some fats, protein and some slow digesting carbs, or something low carb like vegetables or fruits, which have lots of nutrients. The fats that you ate will keep you full longer because it slows gastric emtying. Fat is also needed to absorb vitamins A, D, E and K.
Try to get your fat from natural sources, and don't eat too much of it at one time, but that goes with anything if you don't want to gain weight.
A calorie is just a calorie, but the other conditions in your body that you induce at the time. If your body is looking to rebuild itself it will use the calories to add muscle and glycogen. If you are sitting around eating fries and chips with gravy then it will be used to add fat on to you.
Start with manipulating your insulin. If you eat a large amount of potatoes then a whole load of fat you will be encouraging your body to build fat stores. You raised your insulin level, then dumped a bunch of fat in to the mix so your body will readily store it.
Don't eat too many calories in a day, but make sure to eat the right foods at the right time. Keep to real foods not strange chemicals that try and pass for food. Don't be scared of eating fat, just don't eat too much of it at the wrong time.