You have to assume the fog of war does not exist. The enemy knows exactly what you are constructing, no secretly rushing a wonder. It also means you could have a much better feel for the probabilities of winning a military engagement. You could locally run through several turns, pitting their army against yours to see the most likely outcome. The moment the odds tilt in your favor, you would be incentivized to seize the victory, knowing the enemy is running the same calculus.