Not only are they useful in learning environments, but they also find widespread use in the ML industry. Machine Learning is a very exploratory field, in that the constraints and particularities of a problem are rarely well defined. Oftentimes the data has to be explored and visualized, different approaches have to be tried out, parameters tuned, until a valid solution is found. It is a very iterative process. Jupyter notebooks and their interactive code blocks are perfect for this.