1-Are there any impact on DB2 work areas for deleting stats in PSM?
2-What is the best way to clean PPA stats?
1-When you delete in stats manager for a strategy version you're cleaning up the internal stats manager tables which reside in database PTDB.
PSM specifically does deletes against these tables:PTPS_SYSSTATS_0702, PTPS_STRAT_0702 , PTPS_OBJECTS_0702 and PTPS_MASKS_0702.
When deleting stats no other action is done against DB2 or any other object besides the ones mentioned above.
2-The recommended way to delete a statistics strategy or a strategy version is to use the D line command next to the name of the statistics strategy or strategy version to delete from the 'Statistics Manager Strategy Services panel'