rebuilding world - is "chflags -R noschg *" necessary?

[Anton Shterenlikht]

The fbsd manual states in section 24.7 Rebuilding "world":
http://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/makeworld.html

in subsection 24.7.6 Remove /usr/obj

*quote*
Some files below /usr/obj may have the immutable flag set (see chflags(1) for more information) which must be removed first.

# cd /usr/obj
# chflags -R noschg *
*end quote*

I've never seen a file under /usr/obj/ with immutable flag set.

Why would there be object files with immutable flag set?
Is this step really necessary?

many thanks
anton

-- 
Anton Shterenlikht
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