Big Al:
Here's how to use the Circle of 5ths:
You are used to playing three-chord "Song X" in G (G, C, D). You're at a jam session and someone across the way says "Song X ... in B". Two seconds to join in or not: what will the chords be? Glance at a Circle of 5ths chart, or "look" at the chart in your head: B, E, F#. And you're off.
If you already know this, then you already know 90% of what the Circle has to teach you. Looking at the design and thinking about it can give you a deeper understanding of why some things work and others don't. But it's not necessary.
But it's just a tool. If you've already got the bolt tightened, you don't need a wrench ... except that there might be another bolt.
Josepp:
Ignore the interruptions. Just finish what you intend to say about the Circle and don't respond to the asides ... and the other pedants. *G*
BB,
NightWing