What does the Parameter tab mean in SU01

Parameter has fields that a user wants to get auto filled when he open some Tcode. This field can be filled with proposed values from SAP memory using a parameter ID.

For example, if a user only has authorization for company code 300 and he wants the company code field to be auto-filled in every transaction. For this, a parameter is defined in the parameter ID column. Fields that refer to the data element are automatically filled with the value 300 in all subsequent screen templates.