Seriously though, the SNP is incredibly hard-headed, if they held the balance of power that would not be good.
It'd be a literally endless stream of consciousness around independence, the single market, and other demands, which if they were ignored would lead to another election and a likely Tory majority, just like the SNP caused in 1979.
A pro-Union party can't work properly with hardcore nationalists who aren't fans of compromising. Scotland remaining in the single market and other measures that would lead to de facto independence and disruption of larger rUK trade (worth far, far more to Scotland than external trade according to the SNP government's own figures) is not a compromise and can easily be seen through. If the UK breaks up that's one thing, but doing it de facto and creating two completely separate economies would be absolutely, absolutely pointless. There's no room for compromise with a party that is ideologically opposed to treating the UK as one entity for many purposes.
So a hung parliament that relied on the SNP would be very dysfunctional at best. And don't give Belgium as an example of that somehow working... we're not talking about the leading Flemish nationalist party here; the SNP is well beyond that in rhetoric.
There's no way a hung parliament is functional in 2017 with such a large and rowdy nationalist party, unless the largest party has almost a majority, which can rely on confidence votes from the smaller parties without dealing with the SNP.