Hi Paul,
To my best knowledge, having inbound soft reconfiguration will increase your memory footprint and may increase the CPU utilization slightly as the BGP code will need to crawl through more entries in its table, skipping the ones-would-be-filtered-out. Otherwise, I am not aware of any outspokenly harmful effects.
Then again, if you do not know exactly you need it, you don't need it BGP implementations support the Route Refresh functionality for years now, and turning the soft reconfiguration on does not bring any additional functionality from the viewpoint of re-applying inbound policies.
Best regards,
Peter
