Five-Year Plan is quite useful when aiming for a Science Victory. It combines the effects of Natural Philosophy and Craftsmen, providing additional Science and Production for your civilization to research required technologies and complete crucial projects.
However, since adjacency bonuses are quite weak in the late game, you shouldn't use this policy if aiming only for Science and not Production, which does not have policies that double its yield - in this case, you should go for Rationalism instead.
Civilopedia entry Edit
The five-years plans of Soviet Russia were a series of economic development guidelines devised by a state planning committee appointed by the Communist Party; the first was initiated in 1928 AD, and the last was in operation when the Soviet Union dissolved in 1991. Fulfilling the plan was the primary motivating factor for a Soviet bureaucracy that became unwieldy attempting to do so. However, the initial successes of the early plans motivated other communist nations, such as Mao’s China and Castro’s Cuba, and even some capitalist states to adopt this method of promoting and coordinating economic development. Most have sensibly abandoned such a restrictive and often unrealistic approach.