To control the values available to select in the filter expression, an admin can use restricted values. Users who build the filter expression can choose from designated values only, not a default or blank value. In practice, restricted values are created in Contact Builder. Then when a user creates a journey, the dropdown menu used to set the attribute value displays a list of preselected values only.
Contact Builder doesn't limit the data that is accepted into data extensions according to data type. Not all records in a data extension meet a data value condition set when setting restricted values. Contacts that don't meet restricted values conditions are sent down the Remainder path.