Why load in NPN transistor switch are located in collector circuit?
To make current flow through the base of the transistor, you have to make the voltage on the base about 0.7Volts higher than the emitter.

Connected as you have in the schematic marked "Figure 2," that means you only need 0.7Volts to turn the load on completely.

If you were to put the load between the emitter and ground, though, you would have to drive the base to a much higher voltage in order for the transistor to conduct and power the load.

Since the voltage across the load can vary, you can never be sure just how much voltage to put on the base to make the transistor conduct.  You can also never be sure just how far you've "turned the transistor on." If you were trying to make an amplifier or motor speed control, it would be difficult to control the output since would depend in part on the load.

Another thing to consider is that if you are using a 5Volt signal from a microprocessor to control the transistor, then you might not be able to drive the base of the transistor high enough if you are using the transistor to switch a 12Volt load in the emitter circuit.