identity mapped paging

I am not clear about the use of identity mapped paging while paging is
being enabled by the operating system. Also I don't understand at what
point are the
identity mappings no longer useful.According to this article
http://geezer.osdevbrasil.net/osd/mem/index.htm#identity - "The page table
entries used to identity-map kernel memory can be deleted once paging and
virtual addresses are enabled." Can somebody please explain?

Thanks
Vaibhav Jain
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