If I use an R1 resistor of 100 ohms and an R2 resistor of 200 ohms, I get 6v from a 9v source (for example). The equation becomes (200/300)*9. or 2/3 of the voltage in (12v in would give 8v out; in this scenario). Since the ratio is what gives the over all output. What (other than heat) would be the down sides of using 2k ohms and 1k ohms? Or 20k ohms and 10k ohms? or even 1 ohm and 2 ohms?