I'm a total noob, but after researching Naza-M mode I felt there was little downside to using it, and used it on my first flight. I believe DJI didn't activate it out of the box to keep things as simple as possible for the novice, giving them the fewest adjustments to deal with.
To sum up, in Naza and activating IOC, you are able to use the bottom position of the S1 switch as a Fail Safe setting, so you don't have to turn the power off to get to Fail Safe. Also, with the S2 switch, you can activate Course Lock and Home Lock. When the bird is far away and you lose orientation, you can put it in Home Lock and just pull back on the right stick, and it will return to you, regardless of it's present attitude. I'm quite a few flights away from using Course Lock, as I still don't completely understand how to use it.
This is a pure novice talking, so hopefully someone else can elaborate.