Questions !

I could see a situation where you set it to furthest. ... Might be if you have a Ferris. Weapon that you want to fire a distance away,a layered defence perhaps....   Not sure there is a lot t removing it tho

I'm sorry but I don't understand.  A ferris weapon?   

Just to clarify, a weapon set to nearest will shoot at a ship far away just as well as a "furthest" set weapon.   The only time the targeting setting would matter is if you had multiple possible ships to target.  In which case, "furthest" would shoot at the one that is furthest away... the one that is likely not yet injured and has full shields.
In most cases you want to focus a single target, not spread damage out.   This setting might work as kind of a ghetto "take out shields" setting on an anti-shield gun, but even then... most of the time the shot will be blocked by the nearer ships anyways!