When I'm composing a piece, the first thing I need to know is what sorts of things are going to be in it. I don't mean will there be octaves, glissandos, E flat minor, etc, I mean what are the ideas that I will be considering in the piece.
Now, perhaps you don't know what I mean by that. I wouldn't be too surprised, because the normal way is to think of music as sound, i.e. that good music is something that sounds good. I don't think that's right because I know how easy it is to make something that sounds good. Yet it is more difficult to make good music.
Anybody can invent good sounds. I'm not going to tell you how to do it, because if I do you will go away and become famous and popular composers whom everybody likes and who are very rich!
But this sort of approach is just moving notes around on the page, in my opinion.
To say briefly what the alternative is, I would suggest that it is more about moving ideas around the page. Then what happens when the ideas all hit each other and agree or, more likely, disagree, is what we call music.
So much for that! What I really wanted to talk about is what happens after I have found the ideas. Perhaps this is when I should be writing something down, but I don't.
I can see the music in my head, and that is where the ideas move themselves around on the page. Then they keep moving around, getting thrown away, or just being tried out in case they are helpful. I don't see that I should have to write all this stuff down, since I will only throw it away!
Then when I do write music down, I mostly keep it. Sometimes it takes a long time to get from the start to the writing-down part, but I have several pieces on the go at once (they are cooking!).
When the music is ready, it will demand to be written down. There is no alternative. What would happen if I didn't? I don't know, I would explode or something...
Anyway, it does take time before the piece appears, but that time is being used in instant recomposition (faster than on paper). Why waste time?