Indeed. But if you can do assessment on an ongoing basis, you can eliminate the work for the students that have already mastered a given concept and individually focus the work of other students, so that they aren't wasting their time trying to solve problems that they lack the conceptual foundation to solve (math is often like this, missing 2 abstractions needed to solve a problem undermines the utility of the practice, it will be basically impossible).

I'm not suggesting that it would remove the need for practice. I'm suggesting that it could be used to make the practice more effective, for students that are doing well and for students that have fallen behind.