Not necessarily. Cars with 100mm height can also have a single din unit, and the rest of the space can be left empty for storage.
IMHO, the basic difference/advantages of 2 din systems are;
1. They help give that 'integrated look in many cars like the Aveo, Fiesta, WagonR, i10 and swift which have space for 2-din unit.
2. It is possible to have a CD Unit as well as a Cassette player in a 2DIN unit, not in a single DIN unit.
3. Slightly larger screen(in some cases)
IMHO, the basic difference/advantages of 2 din systems are;
1. They help give that 'integrated look in many cars like the Aveo, Fiesta, WagonR, i10 and swift which have space for 2-din unit.
2. It is possible to have a CD Unit as well as a Cassette player in a 2DIN unit, not in a single DIN unit.
3. Slightly larger screen(in some cases)