High Side and Low Side Mosfet

[EE-MAN]

How's normally will use 2 Mosfet with PWM (High Side and Low Side) instead
of using one Mosfet.

 

[EE-MAN]

I means in DC-DC conversion......

For examples....there are one PWM with 2 MOSFET in VGA Card power circuit
(12V to 2.5V conversion). What's the advantanges of using 2 MOSFETs ?