The concept of economical chords, utilise different chord qualities but with exactly the same fingering on different strings. I have found them quite useful in that you can learn a new chord quality but use the same chord shape. This three examples here utilise four note voicings (different chord quality but same chord shape). There should be enough information here for you to understand the concept, and although some of these voicings can sound a bit strange, in a particular context they can sound great.
The following examples utilise four note voicings.
Amin9, Bmin6, F#maj6.
Eb7, Bbmaj7, Fmaj7add4.
Fmaj7, Bbmin, Ebmin(maj7).
Ebdim7, Bbmin7b5, F7b5.
economical chords
The following voicings utilise;
Amin, Dmaj(min7), F#7b9.
Amaj, Dmaj, Gmaj7#11.
A#9, Dmaj, Gb5.
A#5#9, D#5, Gmaj.
economical chords2
Ebmaj7/A, D7b5, A9/G.
A#5, Dmaj#5, Gmaj7.
A13#9, E7#9, Ab5.
A7, E7#5, Bmaj7#5.
economical chords 3