The key of G used in the example would be applied to the Key of C following the sequence of notes used in C Major (C-D-E-F-G-A-B) 1-2-3-4-5-6-7
1= maj7
2= m7
3= m7
4= maj7
5= dom7
6= m7
7= HD (Half Diminished)
This pattern works in all Major keys and represents 4 of the 5 qualities with 7th chords; maj7, dom7, min7 and HD.
Understand that following patterns give more of a mechanical process to your playing.
In CSchlegel's post, he emphasizes on purpose or function to chord usage and voicing. This only comes with the complete understanding of how the chords function to each other and not by certain patterns. It allows for ways to phrase a piece with originality and resolve. It also opens ideas with the opportunity in modulation.
Look at the dom7 chord for example; In the Key of C, that would be G7
(G-B-D-F), a G Major chord with a m7 interval. This chord creates two dissonant intervals within it that needs resolve; the m7 (F) between the Root (G) and the natural 7th (F#) and the other is the b5 (F) between the 3rd (B) and it's 5th (F#), known as a Tritone (B to F is a Tritone).
In fact, if you were to look at a dom7 chord (G-B-D-F) and sharpen the Root 1/2 step, it would become a fully Diminished 7th chord (G#-B-D-F).
This is the difference between following a pattern and understanding how chords function by voicing. It's a lot to digest at first, but if you focus on things a little at a time, it will fit the puzzle in your own creativity.
