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