I actually just wrote a paper on this. Heavy industry in China actually underwent incredible growth during this period, with heavy industry output increasing by 230% from 1958-60. Global output of resources such as coal and steel increased, resulting in China becoming a global leader in those industries. The number of technicians, engineers, and machines in China also increased greatly. Another possible benefit, that Roderick MacFarquhar examines in Origins of the Cultural Revolution, vol 2, is that the Great Leap Forward sort of "galvanized" the Chinese masses, meaning it gave the Chinese the belief that they could take control of their destinies and "leap forward" instead of sitting under the yoke of nature.

Source: MacFarquhar, Roderick. The Origins of the Cultural Revolution. Vol 2 Oxford: Oxford University Press for the Royal Institute of International Affairs, the East Asian Institute of Columbia University and the Research Institute on International Change of Columbia University, 1983. pg 300-340

Benefits of a completely man-made famine and the death of countless millions? Not many benefits.

The immediate benefits are difficult to calculate because so many died as a result of the 'backyard smelters', not to mention the ecological damage of establishing steel production as a cottage industry.

Only long-term benefit I can think of is, as a result of the GLF, China really cozied up to USSR. Feeling superior, the USSR became aggressive with China- even while sending them aid. It could be argued this habit of aggression towards China by the USSR eventually led to the US rapprochement during the Kissinger years- or at least made Chinese leadership consider the possibility of US rapprochement. Search strategic triangle

edit: added strategic triangle if ppl want more info