COPTFLAGS (not?) only for compiling the kernel?

[platanthera]

[/etc/make.conf]
...
# To compile just the kernel with special optimizations, you should use
# this instead of CFLAGS (which is not applicable to kernel builds anyway).
# There is very little to gain by using higher optimization levels, and doing
# so can cause problems.
#
COPTFLAGS= [whatever]
...

just the kernel... sounds like COPTFLAGS setting should not effect world or 
port builds, but apparently it does.
Or do I misunderstand something?