by xanalor
Thematically it is very well-explained after the turning point.The reason you don't follow-through on the instructions at the time you complete the objective is because they don't want to introduce these particular new information/changes mid-game, and although the objective is mandatory, you still have to complete other objectives. So you're likely to still have more work to do in the game even after getting the hollow men on the havens. Only later (at the end of the game) will you find out what it means.
Mechanically, there is almost no downside to losing population in a haven:
(city drops to 0 turning point spoilers)
[o]A haven can't be fallen, as the rules specifically apply to CITIES, and therefore the restriction on actions available when a city is fallen doesn't apply. The ONLY game effect of having a lower population in a haven is that it will produce fewer cubes when you play Produce Supplies. But even that drawback isn't likely to be a drawback, because by that point in the game you are going to have supply center cities with high population that are much better targets for Produce Supplies, and even a global produce probably isn't likely to fill every last available spot. Really, the only notable impact is (end game spoilers)
[o]How the lower population affects your score[/o]
[/o]
Bottom line, mechanically it's really no big deal if the haven population goes down, and thematically (not really a spoiler, but I'll tag it anyway)
[o]you're ultimately trying to leave the havens anyway.[/o]