Good question. You'll want to use Automated Time Series when you want to forecast multiple future values of a target (for example, when predicting sales for each day next week). Automated Time Series will extrapolate future values in a continuous sequence.
In comparison, you'll use Out-of-Time Validation (OTV) when your data is time-relevant, but you are NOT forecasting (e.g., you are predicting the target values for data that fits on individual rows). Use this if you have single event data, such as patient intake or loan defaults.