If you're China in 1980 or 1990 (ie third world infrastructure), vast infrastructure spend will faciliate your decades-long growth explosion. Without that, you can't become China of 2019, you can't actually go from a $400b economy to a $14t economy. The ports, roads, rail, bridges, utilities, energy generation, et al. is a requirement and produces extraordinary returns in a context like that. It drastically boosts economic productivity and raises your maximum output potential by a lot.

As another recently discussed (on HN) example, Romania has had one of the world's fastest growing economies in recent years. Economically it's attempting to push into a solid middle-tier economic nation, in the footsteps of countries like Poland, Chile or Slovakia. Romania simultaneously has a horribly lagging roads network that is in desperate need of expansion and improvement. It's very likely that properly building out their roads infrastructure would help facilitate their economic boom continuing; and that not doing so, would act as a serious point of friction on growth long-term. You can't get to $25k GDP per capita, with roads built for a $2k GDP per capita economy.