So far controlled starvation actually proved to be very healthy for my grassland settlements. I was way too careful with them, and now 3/4th of the population is removed they produce enormous surplusses, especially once you restore the mill and market (which goes really fast if you are there in time) I increased the food send towards my town elevenfold from a single settlement, who know has half of the population it used to have at best, but has all the same buildings and a lot of output.
Interesting. I know Tom talked about changes so that some region produce better if you maintain their population below "maximum" level to encourged some pure farming settlements, but I was unaware it had been implemented. Previously I never saw production benefits from removing food/population from a settlement, this the only reason to do so was if you preferred to increase the population elsewhere, or needed to for trade.
It's surprising that you haven't had any problems when trading food. I'll experiment with it a bit more and see what happens for me. I've definitely accidentally starved a settlement by taking people out of the fields to build or to train as troops, so since that's never happened to you perhaps there are issues around this with certain settlements and I've just been unlucky in choice of settlements.
I can't really confirm anything without some further testing.
Its all about relative proportions. In some regions taking more then 5% of the population out for building will cause me issues. In others I can dedicate at least 20% without problem. To better assist you I would need to know what type of region, population, militia and what the population is up to. Prospectors are handy here, so you can see the exact base productions, though you can estimate things reasonably enough given food production/population and region size.
Also remember that starving code has changed a few times since the start of this world, and is generally a bit more robust now then previously.