As I have heard innumerable times, "The 'C' in SCA stands for 'creative.'" Yes, that's so. But "creative" does not mean "unlimited license to ignore stylistic conventions."
What would you think if you were a dedicated jazz enthusiast who found a copy of the latest pop diva's album in your section of the music store? You'd think an error had been made. Pop and jazz are different, even though they're both 20th (and 21st) century musical styles and can share instruments and even vocal production techniques.
But you wouldn't know that unless you'd listened to both jazz and pop. If you had grown up on, say, opera, you might not be readily able to distinguish between the two until you'd listened to them a good bit. At first, they'll both be "not-opera." Then you'd start to pick up that the harmonic progressions in pop tend to be much simpler than in jazz, that there are rarely brass instruments in pop, and so forth.
Now let's say you wanted to write some jazz music. Do you think that the best way to start, after having just listened to your first two jazz albums, is to write whatever music comes to mind, toss some improv on top and call it jazz?
Many SCAdians balk at the idea of doing copies of medieval or Renaissance pieces. Our own modern thinking puts a very high premium on creativity and originality, and "just" copying seems stale and boring. But when the artistic sensibilities we are seeking to re-create are so far removed from our modern aesthetic, "just" copying provides a way of getting back in touch with the acceptable styles and techniques of the period.
I like to look to someone like Flory Jagoda. Ms. Jagoda was born in Sarajevo and grew up within the Jewish culture there. She is of the modern descendants of the Sephardim who were expelled from Spain in 1492; their language is still largely understandable by someone who speaks Spanish. She grew up with the traditional music of her culture, and when she writes new pieces of music, I don't think anyone would hesitate to call them "Sephardic." She is part of a living tradition, and she is continuing it.
Most of us are not parts of the traditions we're trying to re-create in the SCA. We're trying to piece together the artistic expressions of cultures that died a long time ago, and in some cases, we have scant evidence as to what was and wasn't a part of those cultures. One of the best ways we have to try and reintegrate ourselves into those traditions is to copy whatever relics have come down to us.
We can't grow up surrounded by Florentine gowns or eating Burgundian cuisine. But we can get a taste of what that might have been like by studying the pictures and texts of the time, making copies of what artifacts we can, and then living with them for a little while. Once we've spent some time doing that, we can get a partial sense of what fits this culture and what doesn't.
Then you're ready to do your own creative work, using the appropriate stylistic "language."
Our hypothetical opera-raised jazz fan, for instance, should at a minimum listen to a great deal more jazz first. For preference, he should also learn some real jazz songs, either singing them or playing them on an appropriate instrument. Once he's got a reasonable repertoire of jazz under his belt, and has a nodding acquaintance with even more jazz, he's much more likely to understand what makes jazz jazzy and to be able to write in that idiom.