Low oil prices are causing the Russian ruble to weaken and in turn is leading to massive, non-monetary sourced inflation in Russia, reducing its standard of living, and reducing the ability of its government to spend on endeavors including its military.
It weaken ISIS which funds itself with oil revenues, it weakens tyrannical governments across the Middle East and North Africa like Saudi Arabia, Iran and Egypt.
It strengthens economies that are based upon expertise rather than resources, like the oil importing U.S. and Japan.
It weaken frackers and oil companies. It helps working people for whom high oil prices are a de facto regressive tax (doubly so in the Northeast where people heat their homes with heating oil), and makes flying on airplanes more affordable.