Especially during early combat. I never invest into science heavily until at least five days in, and never invest into anything but economy until about three days in, or whenever I start needing ship productions.
A good way to think of it is that the later you invest into things that are not economy, the more you'll be able to invest at that later rate. Economy is used to create Industry, which is used to create ships, which are used to acquire new systems, which is the ultimate goal of this game. Build industry early without economy, and you'll have high production in the short term, but unless you can capitalize on that by conquering lots of nearby enemy systems, it'll set you back badly due to your lack of economic strength. At the same time, a lack of industry in an economy-heavy build is a risky investment with potentially very high payoffs.
Abaddon and I in Game 5 provide a good example for what happens when a fast-expanding build runs into a high-economy low-industry build.
