This made me think of typing tutor programs that just prompt for random letters. I type like shit on those-- slow and inaccurate.
On the other hand, I'm quick and reasonably accurate when typing English words and frequently-used command lines.
The analogy would surely hold true with musical instruments. Even with my limited experience playing musical instruments I can't imagine trying to practice random notes and rhythms. On the face of it I would think it would have little to no value. (Effectively practicing to play unlistenable music...)