What are *.xz compressed kernel modules for (Fedora 21)

[Kevin Wilson]

Hi,

I have Fedora 21 (x86_64).
Under /usr/lib/modules/3.17.4-302.fc21.x86_64/kernel, all the kernel
module are in compressed form.
(xz files).
Under
 /usr/lib/modules/3.17.4-302.fc21.x86_64/kernel, the kernel modules
are in the *.ko form

What are the *.xz compressed kernel modules for ? In fedora 20 we had
only *.ko files under /lib/modules.

It seems to me that after booting, when running modprobe, only the
*.ko modules are used.

Just wonder what would happen If I would (accidentally or by purpose)
delete the /lib/modules folder in fedora 21 (I don't intend to do it
before getting an answer here...)

Regards,
Kevin