A pot is basically two resistors in series.
The middle pin (wiper) of the pot is the tap between the two resistors.
You can continiously vary the ratio between the two resistors.
Good if you want a variable signal or voltage.
But sometimes a circuit needs a single variable resistor.
Then you can use one side pin and the wiper, and ignore the other side pin.
The other outer pin (which is basically the other/unused resistor) is usually shorted to the wiper,
because a (dirty/old) wiper can loose contact during turning.
The circuit might not like an intermittend "no resistor connected".
If the pot is used as single adjustable resistor, then you can't ofcourse connect the pot to 5volt AND ground.
Turning the single resistor to zero ohm would otherwise short the 5volt rail to ground.
Leo..