In electronic industry putting two transistors is a method that is often used to reduce the power dissipation across each transistor. 

Watch this YouTube video:

After watching this video do not forget that you do not need a resistor for each transistor. They can share one base transistor and one collector or emitter transistor, depending on the transistor configuration.

However, putting transistors in parallel is not well spoken off. Here is the circuit that I have drawn in PSpice software. Do you think it is a good circuit?

You might have assumed that connecting two transistors placed in series will ensure that each transistor will only need half the maximum collector emitter voltage. However, this is not the case because one of the transistor could be saturated and the other will be dissipating almost the entire power supply voltage from its collector to its emitter if the collector current is low. Thus this circuit is also lacks linear characteristics that a parallel transistor circuit will have. This is why this is a bad circuit for reducing power dissipation.

However, the circuit above can be modified and become useful for other applications. Zener diodes can be placed in parallel with transistors and an LED with resistor can be placed in series with the collector. This will allow four channel control of four LEDs with a 9 V battery. Suppose each transistor has a maximum collector emitter voltage of 5 V (this is just an example because a typical BJT transistor would have maximum collector emitter voltage of 30 V and a typical LED does not need much current/power at all), the Zener diodes will ensure that this voltage is not exceeded even if the power supply voltage is doubled. However, even Zener diodes have maximum voltage, current and power ratings. You can connect four transistors in parallel with a 680 resistor in series with the LED. However, this will lead to power loss, due to power dissipated in the resistor. This is why this modified circuit is could be a better solution the four channel LED controllers or motor/relay drivers.