FA-Clearing Account

Hi,

On natural account form there is a section for clearing accounts, i know cleraing account are just clearing accounts but still what is their purpose here. they will just create extra entries..so why use them?

I'm also aware of that 'you hit the clearing account for the AP invoice booking as well as the FA asset addition entry./tab', but what about retirement? I have also seen the entry from Oracle docs but appreciate if some1 can xplain with double entry i.e. what wll happen if u sell an asset..effect on AR, Ap (for removal cost) etc...