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Like Prajput said, you aim at using composites when you want to achieve the best performance for your product. For mechanical purposes, optimized stiffness (max) and density (min) are often given in product design requirements and for that you might need to use a light metallic matrix for example reinforced with stiff ceramic particles. Then you have both advantages of the ceramic and the metals combined in the same composite materials and it's obvious when you compare to bulk materials in an Ashby chart (Ansys Granta EduPack or Selector) like in the screenshot below for example. In the case of lightweigthing, composites can be really an advantage: https://www.ansys.com/resource-center/webinar/transportation-railway-lightweighting
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