I noticed the computer making fusion as one of his first buildings, and I cannot understand the reasoning on building a fusion over a factory......

with a fusion building with 10% more production, and 12 production for your capital, that fusion building has a maintance of 3, but it only helps production 10%, or 1.2 from your capital. I cannot understand the reasoning behind building it first, unless he knows I'm going to take his planets so is intentionally trying to hurt my economy.......

If i built 10 factories on one planet, my 11th production building would be a fusion or higher level, maybe with less if I was doing better stuff....why build a building with the same maintanence cost as a factory but less productive?