Originally posted by lalimacefolle
Roman numerals are used in studios, so that you can ask the session players to play the progression in the key you want, without having to change the set of sheet music.
There's even particular names for some of those progressions, such as "anatole" (I'm french, it might change in your country) which means the I VIm IV V, and others...
I frequently jam, and some people just call "I IV V in A, and one, two, three, four..." well, it takes less time than calling the name of the chords!!
As to roman opposed to arabic numerals, I guess they are easier to see (less round shapes)

aaahhh i see. they look cool too. hey thats a good idea, for jamming. i only have one jamming buddy ( and he is kinda new at playin and kinda sucks) and usually im just like "follow my riff with some rhythm, and he sits there and watches me...which is the worst thing you can do when your trying to jam with somebody.