Only when you are clear about everything, from paper-format on to the used colours, from the type sizes to the arrangement of the text, just then you should complete your work at the screen. Finally the computer is only a tool (however a useful one) for us composers.
Also a bricklayer should know where the wall is built and how the house should look like later before stiring his morter.You want to continue?
Crash course-
That's my opinion!