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<<<
This is meant as a backward compatibility convenience for those
systems with a bootloader that can't be upgraded to accommodate
the documented boot protocol using a device tree.
>>>
and
<<<
Do not leave this option active in a production kernel
if you don't intend to always append a DTB.
>>>

Meaning that if the loader supports passing DTB, the kernel shouldn't
have an appended one.

Apart from that, if you use an appended DTB, this completely overrides
any DTB passed by the loader, so (unless you also enable the unholy
CONFIG_ARM_ATAG_DTB_COMPAT) you also lose the ability to pass kernel
command line options from the loader.

/
	Leif