Except when they don't, and instead declare wars of extermination, and slaughter those who surrender wholesale. With the predictable consequence of getting their enemies to fight fanatically, and thus losing.
As for exploitation, Germany got more out of Russia and all of eastern Europe by trade prewar, than it ever managed to extract by wanton slaughter in the occupation. A few cameras and some electrical equipment readily bought a quarter of Ukraine's harvest. An occupying army that murdered millions cost more to send, and got no more out, ever. See Milward on the war economy figures.
Your revisionist excuse fantasies about rational Nazis are your own sordid delusions, not history.