Saudi Arabia (and many (most?) of the Gulf States, too, I think) has a serious problem. As in China, the legitimacy of the ruling party, the royal family - House of Saud, depends upon satisfying the needs and wants of enough people. The Saudis, unlike the Chinese, have been poor managers: they have simply spent as though the oil would never, every run out. Saudi Arabia needs oil to be priced at about $100/bbl to balance its bloated (heavy on social services/transfers to individuals) budget, but $100/bbl oil could make America a (temporary)* energy superpower and change the energy power balance in the markets.
Cui bono? As T6 suggests: the American consumer and, that includes e.g. industries and public utilities, too; also China, which still has an insatiable demand for oil; ditto India where demand has been constrained mainly by the high price of oil. Western Europe also benefits for the same reasons America does.
Who loses? Canada? No, not really ... some strain, in Alberta, but Ontario gains, so it's a wash, really, from a national perspective. The Middle East? Yes! Africa? Yes! Venezuela? Yes! Russia? Yes! Yes!! Yes!!!
* There are many reports that the economical output from fracking has a very limited life - I have read estimates as low as 15 years and as high as 50. Contrast that with e.g. Canada's heavy oil which is guesstimated to have a life of 100+ years, even 200+ by some estimates.