Complex sentence: The main difference between both categories is that hard materials are usually unaffected by the heat produced by the machining process and may actually benefit from it, while at the same time being very brittle, requiring sightly blunt cutting edges to avoid fracture.
Split into simpler sentences: The main difference between both categories is that hard materials are usually unaffected by the heat produced by the machining process and may actually benefit from it. The down side is that they are usually very brittle, requiring sightly blunt cutting edges to avoid fracture.