It can drop your CPU temps by 2-3c, maybe more depending on the type. Is it necessary? At todays processor speeds, yes. Some type of thermal material needs to be between the CPU and heatsink. Do you need paste or grease? It all depends if you're going to O/C. If you're running stock speeds, a stock cooler and thermal interface material will do. If you're going to O/C, temp and voltage is life. The cooler the better.