I know too much current will damage/destroy an LED and a current limiting resistor is required.

If supply voltage is 5V and Vf of the LED is 1.7V, there is 3.3V that must be dissipated. Using the formula R=(Vs-Vf)/ILED will give me the correct size of the resistor.

If supply voltage was 1.7V and Vf of the LED is 1.7V, the formula would result in R=0 ohms.

But then there would be nothing to

__limit the current__. Would the LED only draw

__what it needed__?