Issues related to jazz and swing.

Keys:

Which "keys" do musicians want to play? That will always get someone to review the circle of 5ths. My band leader (Tom) is a retired H.S. band director. He worked many years in drum and bugle. He said nobody wants to play in more than 3 sharps or 3 flats. (who wants to keep track of five sharps or five flats?) It makes sense).



Another band leader (also very experienced) kind of reinforced that. He said That he uses Bb and Eb for horns and Saxes and that "nobody ever plays In A or D" so C-F-G keys and the horn keys.

BUT band leaders do not take into account blues players who use the key of E (don't know why). Perhaps because there is lots of slide room)

More -- most female singers prefer the key of A. Male singers like D key. Fiddles and mandolins like A and D (don't know why). Capos can quickly change C and G keys into A and D. Folk music, bluegrass and country use A and D.

Jazz

(this is from Wikipedia):
A common cadential chord progression used in a wide variety of music genres, especially jazz harmony. It is ii-V-I and is nothing new (2-5-1). It has been used for a hundred years and is currently "a staple of virtually every type of popular music," including jazz, R&B, pop, rock, and country. For example "Honeysuckle Rose" (1928),

ii-V-I progressions are extremely common in jazz.