questions about asset move

Hi:

i've been deluded by a problem about asset move for a long time, hope you can provide me more insight about asset move.

why asset move has to be transfered between sub-inventory?

what's the good point of asset move?

what if we have to move a n asset to a location where where is no sub-inventory correspond to it ?

from my point of view, asset move should be inter-department in or between organization, why it has to be related to sub-inventory?

im looking forward to your response

thanks in advance!