MPPs came in handy in my current game (Persia on Monarch level, continents). There are 2 main continents, one of which I own completly while the other is split evenly between Japan and Rome. Problem was, by the time I swept England, Zulu and Babylon from my continent I was behind in all areas -- techs, culture and militarily. Also, my rep. was none too good due to my early war-mongering. My only chance to catch up was to foster a war on the other continent, so I did some major sucking-up until Japan agreed to an MPP. Rome declared war on me, and the big boys proceeded to duke it out. They both changed to war govts. which allowed me to catch up in all areas -- I managed to beat them to both Univ Suff. and Hoover, and have open options on the type of victory I want. Without MPP I stood a good chance of being invaded by both civs, and would have had no chance of catching up. But I was lucky that Japan and Rome were evenly enough matched to lead to a prolonged war with no clear winner (or else I would have been in trouble).