What makes a custom recovery stay?

Hi,

According to many articles I've read, stock Android rewrites the recovery partition with a stock recovery image at each boot. So to make a custom recovery stay we're asked to remove a file called "recovery-from-boot.p" in /system which does work.

But WugFresh's Nexus Toolkit flashes a file called "perm-recovery-signed.zip" to make it say. And to revert to stock recovery, it downloads and flashes the stock recovery image and then flashes a file called "undo-perm-recovery-signed.zip".
I'd have guessed just flashing the zip would make the ROM replace the Custom Recovery with the Stock version. Why does it flash the recovery? What do these files do?

Clarification is appreciated.
Thanks.

Which of the latest Verizon flagship phones makes the best ROOTED phone?

Hoping I've found the right forum for this question, feel free to move if I have it wrong.

So after two years with the Galaxy S4 I'm back on the market for a new phone. Of course shortly after I get any new device I find myself making the trip to xda to see how to hack my new toy.

I can search all the reviews until my fingers are sore from typing, but what they don't really tell me is which of these phones really shine after they are rooted. I'm hoping the community here has an opinion on that. What say you?

Lg g4 new firmware h81510dpre rooted+greenify+viper audio makes my lgg4 awesome......

Best firmware so far no issues at all....pretty decent battery life....