The benefit of stepping down the voltage of the battery is that we can give a constant/stable performance for our devices until the battery runs out the power. That’s only one example of voltage regulation, actually there can be more advantage depends on your need. Here is one example of voltage regulator circuit constructed from discrete components:

5v from old cells circuit schematic

This is a circuit that is used to get 5v from old cells. This circuit is used to replace 78L05 3-terminal regulator. The circuit can generate a constant 5v  @ 100mA from any old cells. This circuit uses 8-cell holder that will give voltage about 10V and will operate down to about 7.5V. This circuit has good regulation at 10V, only dropping about 10mV for 100mA current flow. The output drops from 5V to 4.8v on no load and 4.6v on 100mA current-flow. The voltage drops can be compensated by adjusting the pot. [Schematic diagram source: talkingelectronics.com]