I've been playing Mercenaries 2 the past couple days. One interesting feature is how allied and employer factions are in possession of resources you need, and you can take those resources at any time. By completing missions for those allies, you can earn rewards like special airdrops. But you can also take oil and money from them, albeit angering them in the process.
It reminds me of Neverwinter Nights. In that game, some NPCs offered quests or items, but you could also earn experience points by killing them. One reward could replace the other, or you could find ways to achieve both.
In any case, it can be a fun scenario when an NPC or faction has resources the player can only obtain by force and opposition. It's particularly interesting when the game challenges the player to stick to good and friendly actions, because evil is the easier way.