135. ivaL sannidhiyAle kAkam thalai peRRathu; athillAmaiyAlE rAvaNan mudinthAn.
Because She was with Sri Rama, the crow (kAkAsura) which committed the greater sin survived. Because She was not with Him, Ravana who committed the lesser sin (compared to the crow) was killed.
Sri PBA Swami's Sarartha Deepikai:
That Her mediation is required can be seen even during His vibhavAtAra.
During the Rama avatar, the crow (Kakasura) committed the gravest of sins against Sita. It should have become the target for the Brahmastra sent by Rama and been killed for its sin. Instead it became the target for His grace and was saved, because of the presence of Sita next to Rama. Ravana who committed a lesser sin, however was killed by Rama's arrows, because of Her separation from Rama.
Thus far, the "srimad" term has been explained.