I was looking for a previous thread, where someone gave an example that made it very easy for anyone to understand why we need "good" fats in our diet. I couldn't find it, so I'll repeat it.
Your body is a building, and they're are little construction workers inside. They need bricks, barrels to carry the bricks in, and mortar to make the bricks stick. Protein are the bricks, carbs are the barrels, and fats are the mortar. If the workers don't have all of these materials they won't be able to make a proper building, they also need quality materials(healthy foods) so they can build a strong building (body).
Hope this answers your question.