Allow a file (a kernel image "zImage") to be inserted
into the file system in such a way that the inserted
image file is VERY eacy to find by a VERY limited boot
loader.
Bootloaders need kernel location (usually an offset in
file system) and size of the inserted file to be able
to copy the kernel into RAM for booting it.
By inserting kernel image into the file system itself
it is possible to make storage space usage more efficient
See example in CramFS (see -i option):
http://www.ussg.iu.edu/hypermail/linux/kernel/0012.1/0002.html
http://docs.linux.com/print.pl?sid=02/10/08/1912218
Has some toughts on kernel and file system placement.