This rule was designed to stop spying. Someone would take note of where either a CV or NOE was located, then switch sides, up buffs or fighters and take advantage of that by sinking the CV or busting the NOE.
In one sense, who cares. During WW2 espionage was a big deal, it happens. AH then decided it had to be addressed. 12 hours was overkill. Make it 15 minutes, 20 minutes tops. That small penalty window removes the instant advantage of switching sides, though ends the torment of 12 hours. On a side note, switching sides to find a fight is harmed by even a 15 minute window. I strongly suspect this rule has helped - not caused - but helped the decline in numbers.
boo