Regarding resistors in series vs parallel
In a normal situation - lets call it a DD circuit.
Series - will add a resistance to the whole circuit, reducing overall current draw. Since current passing through each component in the series circuit is the same, the LED will be receiving reduced current draw.
Power in watts is the current multiplied by the voltage drop across each component. The emitter will drop between 3-4V depending on what it is, and what current flows, the resistor can drop any voltage depending on its value.
Parallel - The resistor is effectively independent of the LED because current can flow both "circuits"; the LED or the resistor. Remembering that current draw is determined by the resistance of each circuit, the LED will draw its own current, the resistor will draw its own current and will not affect each other.
With an ideal power supply, the resistor will simply draw current, and make heat. The LED will also do its own thing, as if there was no resistor. So essentially all thats happening is that more power is being drawn
This changes however in a Current Controlled circuit. If your circuit is able to run in regulation, and has enough voltage excess, the 'better' way to reduce power to the emitter is to put a resistor in parallel with the emitter, because the total current flow is limited to X amps. A resistor in parallel will in this case be dividing the current.
A resistor in series will be increasing the total resistance (voltage drop) of the circuit if driven by a constant current driver, and will increase the power draw at the battery end to deliver the same current output. So in that case we will be pushing the same current through the emitter and the resistor. We will effectively just be creating more heat in the resistor, with no reduction in current to the emitter.
The only reason why this is confusing is because we are using current controlled circuits, it reverses the ideas sometimes. This is an example where it can be sometimes counterintuitive. Like for example, when I want to measure the current output of these drivers, I just select the amps setting and short out the driver (only TRUE CC drivers) with the DMM. This short has a very low resistance and normally lets lots of current through, but in a TRUE CC driver it will effectively be drawing almost no power to maintain those 3A. If the driver is not a true CC driver, it will let more amps through and possibly die..
On the other hand open circuits are destructive to TRUE CC boost drivers, with the boost voltage potentially rising very high and killing itself.