User-specific parameter:
They supply defaults to R/3 fields. If a field is indicated, the system automatically fills in default value. Depending on the field definition, the entry can also be replaced with a value entered by the user. (Concept of PARAMETER ID)
You can fill fields on screens with default values from SAP memory using parameter IDs.
For example, a user only has authorization for company code 0001. By entering the value '0001' in field COCD in the Parameter register in this user’s master record (SU01), the system automatically fills the field Company code with the value ‘001’ on all screens he or she calls. If this company code is not predetermined using a parameter ID in the user master record, the system automatically adopts the first value entered by the user at the beginning of the transaction for the rest of the current terminal session. However, this value has to be re-entered the next time the user logs on to the system
Fields on screens are only ever automatically filled with the value saved under the parameter ID of a data element if the Set Parameter/Get Parameter attributes for the corresponding fields have been explicitly set in the Screen Painter.
Choose Tools -> Administration, then User maintenance -> Users. Enter the IDs you want in the Parameter register during user maintenance