Open voicings split the chord across both hands: the left hand anchors with root and 5th, while the right hand plays the colour tones (3rd, 7th, and extensions). The 5th in the left hand adds stability that rootless voicings lack, while the right hand adds harmonic interest.
LH: root + 5th (octave 3). RH: 3rd + 7th + extension spread across octave 4-5. The 5th may be omitted for chords with altered 5ths.
When you want a full, stable sound with both the root and harmonic colour present. Good for medium-tempo tunes and accompaniment where you need more body than a shell but more openness than close position.