Asked about Tuning, in order of what matters
Why do you need a validation set separate from test?
An answer that works
Because tuning decisions leak the score they are based on into the model. With enough trials you find a configuration suited to that specific set. Validation drives decisions; test is touched once for the reported number.
Reading an answer is not being able to give one. The section that teaches this is Tuning, in order of what matters, 6 hours of Hyperparameter tuning.
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