thermal paste is needed to make your processor cooled and not overheating, if your processor or CPU did overheat then it will turn off suddenly, leaving you wondering what’s going on with your computer. a desktop PC need to have its thermal paste renewed every once in 3 years. this is needed so that the heat will be transferred easily between the processor and the heatsink. so the hot air will flow freely.
I bought below thermal paste for the cost of Rp 15.000 or approximately $1.5 dollar. very cheap though yet very important for your PC health
based on wikipedia explanation
Thermal grease (also called thermal gel, thermal compound, thermal paste, heat paste, heat sink paste or heat sink compound) is a viscous fluid substance, originally with properties akin to grease, which increases the thermal conductivity of a thermal interface by filling microscopic air-gaps present due to the imperfectly flat and smooth surfaces of the components; the compound has far greater thermal conductivity than air (but far less than metal). In electronics, it is often used to aid a component’s thermal dissipation via a heat sink.
so you can conclude it yourself that applying the thermal gel between the surface of your CPU and thus your heatsink will better dissipate the hot air produced by extreme uses of the processor. think of it as a better ventilation system for your CPU. such as the central processing unit (CPU) of a personal computer, generate sufficient heat to benefit from the use of thermal grease to improve the effectiveness of a heatsink.