Hi,
the answer is simple: because it has to be done.
refer to help.sap.com or the hana manuals
"The CLEAR LOG command prevents the recovery of entries from the log area. No log entries from the log area are replayed, and the log area is initialized. As a consequence, the content of the log area is lost.
If they are needed, the log entries from the log backups are replayed.
CLEAR LOG must be used in the following situations:
- The log area is unusable.
- You are recovering the database to a different system. "
It just initializes your log area to clean up the not needed log segments of the source db.
Regards,
Jens