As you know, it is possible to omit non essential notes from chords. Any type of 7th chord can be implied simply by playing the 3rd and 7th. These are the guide tones - the 3rd tells you whether the triad is major or minor, while the 7th tells you what type of 7th is used above the triad. In the case of a m7b5 chord and a dim7 chord, the 5th can also be a guide tone, but in major, minor and dominant 7ths, the 5th can be omitted. Using guide tones makes it possible to create smooth chord progressions. The 3rd of one chord often progresses to the 7th of the next chord and vice versa as shown here.
Some interesting voicings can also be created by doubling one of the guide tones.