The Economist:

One reason is that cars are packed with more and more components, demanding more and more electrical power. A modern vehicle may have as many as 150 electric motors. But there is a second reason for the increase, too. Extra voltage lets engineers design cars in novel ways that boost engine output and efficiency. This can be used to make hybrids on the cheap (some people call them “mild hybrids”). These employ a combination of electric motors and combustion engines to cut both fuel consumption and polluting emissions.
 The first production car to use 48 volts is the SQ7, a new luxury sports-utility vehicle made by Audi, a German firm that is part of the Volkswagen Group. It is not a hybrid, but it employs an electrically driven 48-volt turbine to force extra air into the engine when a spurt of power is needed. This provides a faster response than a turbocharger, which is operated by the vehicle’s exhaust gases. The car also has a 48-volt active suspension. Again, this improves response time, permitting faster action from the electric motors that control how the vehicle rolls on corners.