What's the differences of these usage of PNP, NPN transistors?
The two circuits on the left are emitter followers. The BJTs operate in forward active mode (assuming \$V_{in}&lt;V_{cc}\$). The two circuits on the right are common-emitter switching circuits. The BJTs may operate in saturated mode.

When operating in saturated mode, the power consumption of the BJT can be substantially lower than when in active mode. This leads to less self-heating of the BJT, and probably a longer operating life.

Note my use of "may" and "can". This all depends on the resistor values being chosen appropriately for the application.