Question About Blognomic Norms

This is prompted by the Prime Minister seat being recently thrown open to the public. The PM has a veto, and since it can't be overrided except by CfJ thats a pretty weighty stick to have. What circumstances warrant a veto? Would protecting the narrow interests of the PM be enough (say, Veto a rule which he thinks will eventually harm him personally)? If someone were to gain a commanding lead in EV and pass a rule allowing them to declare victory, would that be appropriate to veto? If someone were to propose a rule that proposed a fairly radically altered the flow of the dynasty (say, abolished EV) would that be appropriate to Veto?

Just asking, because I hope to be Prime Minister one day (sadly, looking at the fact that I only control less than 5% of the EV out there, it probably won't be anytime soon -- maybe in the next dynasty, or the one after that).