Cryolite is used in the extraction of aluminum because it helps lower the melting point of aluminum oxide. Pure aluminum oxide melts at a very high temperature (around 2050°C), which would require a lot of energy.
By adding cryolite, the melting point is reduced to about 900°C–1000°C, making the process more energy-efficient.
It also increases the conductivity of the molten mixture, which is important for electrolysis, the method used to extract aluminum.
In short: Cryolite makes aluminum extraction easier, cheaper, and more efficient.