I have never combined raw and kibble because i read and was told that since kibble is slower to digest, it can lead to raw food lingering more than appropriate in the digestive tract and therefore starting to spoil and breed bacteria. Raw digests quickly in dogs and hence why dogs can eat all that meat without worrying about the bacteria in it - kibble blocking the raw from properly digesting is suposedly negating dog's ability to quickly digest raw.
Thats the info i got when i was switching from raw to kibble.... personally, i am not aware of any benefits/reasons for mixing...
Monkey and Amy (cats)
“Dogs believe they are human. Cats believe they are God.”
"The average dog is a nicer person than the average person."