Hello,
Given two ends and one wiper for any 'regular' pot, one end is connected
to the wiper and this makes the pot a variable resistor as the resistance
between the other end and the wiper changes as you turn the shaft.
Of course you can get this action another way...without connected one
end to the wiper. In this way, you can use either end and the wiper for
the variable resistor, and it works the same as above.
So why go through the trouble of connecting one end to the wiper then,
if you can get the same variable resistance without doing that?
The answer is, to lower the noise pickup of the circuit. With one end
completely open it is more susceptible to noise pickup.
This works especially nice if you can ground the end that is connected to
the wiper.