That might not have been the best example.
A guess a more useful example would be that after building a
complicated selection to isolate a portion of an image (say the sky)
the user wants to save that selection, then modify the entire image
(say gamma correction, or colour balance, even desaturate) then load
up the original selection quickly to perform another action on it.
I guess it is a question on that the point of the channels is. Most
people I know who actually use them, use them as "named selections"
that they can work with later. Very few that I know actually perform
any editing on them directly, partially because, as David pointed out,
directly editing channels is awkward and confusing, and using
quickmask is much easier.
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