The difference is that after println, the next line of code runs in a world where the previous println happened. After a Pure.println, the next line of code doe

The difference is that after println, the next line of code runs in a world where the previous println happened. After a Pure.println, the next line of code does not run in a world where the previous println happened, because it didn't and can be revoked at any point in time by later actions, affecting the ultimate outcome of the program (so that maybe that particular Pure.println call never prints).