while i basicly agree with you - there is a good reason for that rule in terms of getting to any results in fights. - its hard to tell if someone is shield running or catching up or retreating - hence, we have the no cruise at all rule.
if you d say, cruising is allowed in specific circumstances, - you d end up in discussions about the intentions of the person cruising. cause some might say he was retreating, some say he was catching up - and some might say he was just flying a generous circle to replenish his shields.
while not such a big deal in fightercombat ( allthough - when you consider VHF vs. LF ... still a considerable one ) - it can become a little problem in capital ship fights.
be asured that i m a bad pilot, - but i d invite you to have a go at a battleship without the battleship ever shooting back at you - and you d never take its shields down if the capital ship was allowed to cruise. while its of course plausible and realistic to do so - the longevity of warships is unproportionally increased by that. ( even gunships can benefit from it, - basicly any ship thats relies more on shields than on hull / agility )
the no cruise rule is made to make things easier. there is no other reason for it but to make it easy to understand for the players. - more exceptions = more difficult situations. - and nothing is worse than having to have 100000 rules in your mind every time you fight someone.