Regarding RSEA:
I actually see it this way.
The whole visa process is already not a cheap one. We have to allot good amount of money for IELTS, EA assessment, Visa application, NBI, medical, etc. Looking at the whole picture, it should not hurt us anymore to allocate few more hundreds of dollars for RSEA.
It's for our peace of mind, as many rightfully said. The whole process is already mind-torturing and we may become too anxious while waiting for that approval. Having RSEA is simply one less reason for being paranoid.