Capricorn I know that they are used to determine the sharps and flats in a key but do they have any practical use?
Renesongs In simplistic terms, If you want to write a song with more than 7 different notes and chords then you need to change keys. The circle of 5ths indicates which keys are most closely related i.e. if you change from the key of C to G you need to change only one note namely F which becomes F#. Changing keys in cycles of 5ths is very common in jazz.
jakjak The best interactive circle of fifths ive come across on the net can be found here. Its very useful. http://randscullard.com/CircleOfFifths/
