Knox is triggered once you root the phone. This is what you will see in DOWNLOAD mode
Many users are worried about warranty once knox is tripped as it cannot be revert back to default. You can remove root through supersu pro. My personal experience with Note 3, I could claim warranty without any issues. And based on what I had read in Note 3 thread there are too several users who reported claiming warranty even with Knox tripped
It seems the Samsung service center doesn't check on this Knox stuffs ??
Anyway is your choice and be concerned if you are worried about warranty issues. Just don't root if you wish a secure warranty path

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ALL Kitkat phones faced this problem due to Google restrictions on writability onto ext SDcard. I had used so many different type of KitKat phones and each has its own set of peculiarities. But is a easy problem to solve. Root the phone installed nextappSDfix and you can freely write anything onto the external Sdcard
I cannot answer you whether the default file manager app has any issues writing onto ext SDcard as I rooted the phone within an hour of purchase. I installed nextappSDfix after root

Later date will not change this fact that this is a Google problem. Unless Google remove it in Android L

You mean the writing to SD Card issue?  This is Android issue, same to Sony.  I still holding Sony Xperia  ZL.

Every manufacturer already did it capable write to SD card with condition you must use manufacturer stock own apps.  Third party from Google Play won't work unless the phone is root.

Except for One+One n Oppo all rooting on any other Android will void warranty. Unrooting Sony is even more tedious process.

I had been declared a Samseng fag in ip6 thread just because I mentioned this Note4 UI is smoother
That forumer ask me to go back to my cave
And here he said he want to buy Note4
Some guys simply unbearable

Sony is worst if u think knox is bad . Unlocking bootloader automatically delete some DRM keys . Some of the functions are gone for good unless u backup the folder 1st which is hard to do without root .