Cross-validation estimates model skill by repeatedly splitting one dataset into training and validation sets. Repeating the split reduces sensitivity to which examples happen to land in each set, making the estimate more reliable than a single split. section 4.1.2
The trade-off is cost: repeated evaluation takes more work than a single train-validation-test split. It is more common in traditional machine learning, where evaluations do not incur language-model call costs; use it where the added reliability warrants the expense. section 4.1.2











