You can use no copy when there is no advantage to having the source data physically copied to the target data. Take a scenario where you have a 10TB database. Each day the DB is cloned and mounted to a reporting server. So the clone is never needed for recovery, just reporting. With the nocopy, the 10TB is not physically being moved at the back-end every day (except to copy the pre-updated version of the source device tracks/extents when an update is made) saving lots of array resources. You are correct in your last sentence, whenever you want the target updated to reflect the current state of the source, a new activate is required. The target device will ALWAYS represent the sate of the source at the time of activate. It is the activate the provides the point-in-time.
While running TF/CLONE  with NOCOPY option, Data on Source Volume is not being copied/visible on Target Volume whenever there is a change in data on Source Volume.  Seems I had configured all the required as per the documentation of TF/CLONE.   Appreciate any help    On target drive/volume, I didn’t observed those updates of text file(s) automatically ( without again performing symclone establish / recreate-activate   I had verified the same on Linux Host as well.  On Linux host after adding  and modifying existing data on source volume, I did ran a 'sync' command , did a unmount/mount. All I see is only the files that were copied initially as part of step 4.   Following flag was set: SYMAPI_CLONE_COPY_ON_WRITE = ENABLE  ( restarted all services using stordaemon  CLI )   ----------------------------------------------------------------------------  #symclone -g srini_clonedg_276 query Device Group (DG) Name: srini_clonedg_276 DG's Type             : REGULAR           Source Device                   Target Device            State     Copy --------------------------------- ---------------------------- ------------ ----                Protected Modified                Modified Logical   Sym  Tracks    Tracks   Logical   Sym  Tracks   CGDP SRC <=> TGT  (%) --------------------------------- ---------------------------- ------------ ---- DEV001    1956     15636        0 TGT001    1957        0 .X.. CopyOnWrite   52   Total           -------- --------                --------   Track(s)         15636        0                       0   MB(s)            977.2      0.0                     0.0   # symcfg -version     Symmetrix CLI (SYMCLI) Version       : V7.5.0.0 (Edit Level: 1604)     Built with SYMAPI Version            : V7.5.0.0 (Edit Level: 1604)     SYMAPI Run Time Version              : V7.5.1.0 (Edit Level: 1655)     SYMAPI Server Version                : unavailable
TF/CLONE with NoCopy option - Unable to view data on target volume after update 
on source volume