Questions about the usage model of Block device removal

Hi, list

The requirement of Block Device Removal is described as follows:

The Linux kernel should allow removal of a block device while it is in
use without degrading reliability of the system.  The block device shall
be removable even if in use by an open file (fdisk /dev/sda), a raid
volume, or a filesystem or multiples thereof.

The first question is: Does this requirement include "surprise removal"?
That is, when the block device is surprise-removed, we should guarantee
the reliability of system.

My second question is: what's the purpose of removing a block device in
use? Or who would remove a block device in use for what purpose? If it's
for displacement, then the new disk will not contain the data on the
original disk; if it's for maintenance, the removed disk will be back at
a later time. Right? 
May I know a practical usage case of block device removal from telecom
area?

Thanks,
Forrest

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