When to use Pot vs LM117/317 schem included.

This is just a generic question, but the answer would help me understand some things about electronics. When is it important to use one of these chips as opposed to just the 5K pot at R2 to control voltage?

What voltage are you trying to control? Vout or the voltage at the junction of R1 and R2?

If you just want to control the voltage at the junction of R1 and R2, you don't need the LM117. However, this voltage will change a lot as you try to power things from the voltage. For example, without the LM117 you adjust R2 such that the voltage across it is 5V. Then you attach an LED across R2 -- its voltage will change. The voltage divider formed by R1 and R2 isn't intended to supply current.

The LM117, however, IS intended to supply current and its output voltage Vout will change very little as the current changes (the current drawn by whatever you hook up to Vout). The resistor R2 in the circuit you drew adjusts the voltage Vout.

The Quick Shield: breakout all 28 pins to quick-connect terminals

Awesome, thanks for explaining it to me. I don't have any current intended uses for it, I just wondered when (your LED example was perfect) it was a good idea to use such a chip, as it is a simple enough schematic that I understand what it does and how it works, but did not know its its intended application. Thanks!