Now that you're convinced the four related dominant scales are interchangeable when soloing, take a look at how easily you can combine the associated dominant 7th chords to create altered voicings. Each pairing will have two common tones as well as the two new altered tones introduced by the superimposed chord. The advantage of learning altered chords as related chords voiced together is that the voicings are really easy to invert. Large altered chords can be difficult to play and to remember: Many players wind up learning only a couple of voicings. Grabbing smaller chords also makes it easier to add a rhythmic dimension to your comping.