Obviously, you want to choose what you're repeating. While practice is an essential part in making a project go, you don't just want to repeat. You want to learn from what you do, so that each repetition is not a precise repetition, but is some sort of refinement or alteration of the previous iteration: each time through should provide some sort of advancement.
If each iteration does not include some sort of change then there's the obvious problem of getting bored. Writing is not an assembly-line job where one repeats the same action time and time again.
If each iteration is identical, there's also the problem of not actually getting closer to your goal. If you haven't reached a goal and you want to, then something has to change to allow you to reach that goal--your practice has to change in some way--even of the only change is what you focus your attention on.
So the process of writing contains cycles of repetition--for example in terms of writing and then rewriting a draft, or in terms of sitting down each day to spend a certain amount of time writing, or to write a certain amount. It also contains growth: we can try new things, new ways of saying the same thing, new ways of structuring our presentation.
The endless repetition, therefore, is in the process, but with the attitude that we can learn, then we begin to repeat and refine, allowing us to move towards creation of superior products.