ArduPlane LOG_REPLAY parameter

Hi everyone,
LOG_REPLAY caught my attention while examining the parameters related to logging. After that I set LOG_REPLAY=1 and implemented the instructions in this site .
A new xxx.BIN file created and it is a little bit different for EKF messages. There are NKF[0], NKF[1], NKF[100], NKF[101] etc. What are these? What should I understand these values? Actually, What are the advantages of LOG_REPLAY?

Thanks for answers!