Roddey: Rootless chord voicings result when the root of a chord is 'implied' by other notes in the chord, mainly the third and seventh. By omitting the root, it also allows your free finger to play ather chord tones such as the 9th,11th, or 13th, providing more spice & variation.
In drawing and painting, an artist may imply the outline of a figure with only the shadows, allowing the mind's eye to fill in the rest. Rootless voicings imply the harmony so the root isn't missed. Many musicians are habit-bound playing root-position chords and think it necessary to fit all the information about each chord into every voicing. To simplify, and make the art of chord melody playing more musical, the main consideration must be the melody. Then add the third and seventh of the chords, where rhythmically appropriate.
In a common ii-V-I progression, the seventh of each chord moves chromatically — and smoothly — to the third of the next chord. These guide tones communicate the progression via the voice leading of the seventh to the third. This motion is the most common sound in traditional harmony, and you only need these two notes to capture the essence of the progression. If you're really interested in exploring rootless chord voicings, check this out:
http://www.cs.hmc.edu/courses/2002/fall/mus84/rootless.6.pdf I learned about 'rootless chord voicings' when studying with legendary jazz pianist, music educator, & author Mark Levine, who has written an excellent book entitled the "Jazz Piano Book" which covers 'rootless jazz chords' in detail:
http://www.shermusic.com/jazzpno.htm Ok, perhaps I said too much.
I'll shut up now.
Scott