One effectively sets all the existing subfile records to blanks and zeros, the other removes existing records
SFLINZ (Subfile Initialize) keyword for display files
Use this record-level keyword on the subfile control record format to specify that the OS/400 program is to initialize all records in the subfile on an output operation to the subfile control record format (identified by the SFLCTL keyword). The fields in each subfile record are initialized to blanks for character type fields, to nulls for floating-point type fields, to zeros for other numeric type fields, or to the constant value specified on input-only fields if the DFT keyword is specified.
When the subfile is displayed (on an output operation to the subfile control record), all records in the subfile are displayed with the same value. Any record previously written is overwritten and no longer has its earlier value
SFLCLR (Subfile Clear) keyword for display files
Use this record-level keyword on the subfile control record format so that your program can clear the subfile of all records. This keyword differs from the SFLDLT keyword in that the subfile is not deleted. It differs from the SFLINZ keyword in that after being cleared, the subfile contains no data. Clearing the subfile does not affect the display. However, after being cleared, the subfile contains no active records.
This keyword has no parameters.
When active records already exist in the subfile and all are to be replaced, your program can send an output operation to the subfile control record format after selecting SFLCLR. This clears the subfile and permits your program to write new records to the subfile (by issuing output operations to the subfile record format while incrementing the relative record number). Issuing an output operation to an already active subfile record causes an error message to be returned to your program.
If SFLCLR is in effect on an output operation and no records exist in the subfile, SFLCLR is ignored