Just like Readers, feature types have their own set of parameters that control how that feature type (for example, layer, table, sheet) is being read. They are located in Parameters tab in the Feature Type dialog, or if you have enabled View > Windows > Parameter Editor, it will be docked inside Workbench):
These parameters apply only to a single feature type, whereas a Reader parameter applies to all feature types.
For example, when reading some database formats, there is a Feature Type parameter that defines the name of the spatial column to read.
This is a Feature Type parameter because each table might have a different geometry column name, and therefore each feature type needs a way to define it.
Note that there is no authentication parameter at the feature type level because authentication is a Reader parameter: it applies to the entire database, not the individual tables.
Feature type parameters provide a degree of individual control over reading different layers or tables.