The bass player is playing a low G; what shall we play? We could play a D; that would leave the third undefined, and the listeners' minds would fill in the blanks with whatever they feel right now. Or we could play an F; down low or up high it would create a tension, suggest moving to a comfortable C along a bluesy highway.
We could play a B flat, take it minor, make it a little sad. Or a B natural, move it to a positive feeling, if that's called for. Or an A; the tempered A is a little out of tune to the natural A, but it's still clear enough to suggest harmonic movement. Or an A flat, which would create an almost unbearable tension, and suggest an incompetent punk or a masochistic free jazzer.
But let's keep it simple, and also play a G. Reinforce the bass note, up an octave or two. The note becomes more powerful; perhaps we're rocking out a bit. We could play the open G string: the lowest of the unwound strings, it has the most complex audible harmonics, and might suggest a folky flavor. It sounds almost comical compared to the other open strings. Or we could play the G on the fifth fret on the D string: it's wound, and has a very different sound than the open string, darker, blending better. Or even the G on the A string at the 10th fret; towards the middle of the string, it is full of odd harmonics, and emphatically more bassy, taking us towards a jazzy feel. Or we couFOR GODS SAKE SOMEONE HAND ME A COWBELL!