By default,
new rows are appended to an existing compressed SAS data set. If
you want to track and reuse free space by deleting or updating other
rows, use the REUSE= data set option when you create a compressed
SAS data set.
REUSE=
has meaning only when you are creating a new data set with the COMPRESS=YES
data set option or system option. Using REUSE= when you are accessing
an existing SAS data set has no effect.