Inactive Tutor answered 07/01/19
Six-four chords are naturally unstable in the classical world because of the perfect fourth on the bottom, that being said, in the jazz world chords are often stacked in fourths, so those same rules of tonal harmony don't apply. Six-four chords are most often used as part of a cadence, and it is most often a good idea to resolve them because of their inherent instability.
Hope this helps!
Jake