If you already have concepts of training and validation error then you're already there. The risk is not realising you can't test on your training data, or more subtly that you can't tune hyperparameters on your test data.
True, but I guess it depends on the person. Was just trying to give HN a view of how I write code. I've found it to be faster, but I go in knowing I will be doing a ton of googling.
