3.3V Chips are all of these things... (over their 5V counter parts)

1) Smaller circuit features possible to lower chip node capacitance and achieve faster operation.

2) Smaller die size results means more chips per wafer so costs can be lower.

3) Smaller die increases yields which lowers costs.

4) Power density in a chip on a per unit area is lowered with 3.3 V operation and so the chip is cooler for the same circuit. This advantage is often exploited to permit more circuitry to be put in the same package without increased total power density.

5) Lower voltages on chips lowers the electric field that is generated across silicon dioxide or poly silicon insulator layers between a conductor and the substrate. This in turn can make the chip less susceptable to mortality caused by metal migration through pinhole defects in the insulator layers.

Michael Karas