For me: anything involving data (data scraping, exploratory data analysis, plotting, testing various machine learning techniques, etc); here short feedback loop

For me: anything involving data (data scraping, exploratory data analysis, plotting, testing various machine learning techniques, etc); here short feedback loop is crucial + it's great to have plots in place. Also (a bit) for playing around with new libraries / databases etc. (Much better than both Python scripts (need to be rerun from scratch) and Python shell.)