Master Data Import makes mapping selections for you automatically when it picks up on and remembers selections from prior imports. For example, if you imported into a User Controlled Attribute for the Product dimension. The next time you do an import with a file that includes that dimension, automatic mapping will set the column for that dimension to Product in the mapping preview. Automatic mapping can save you steps in the import setup process.
You can change mapping selections using controls in the top two rows of the Data Mapping preview.