To make a small addition onto what Flevance said, hammer overflow no longer matters negatively. In normal and even more quick speed, you could reach the point where your HE city and your IW city create more hammers than the units cost. In this case, the overflow starts building up and gets to the maximum point. On marathon, you'd have another unit instead of the overflow.
I love marathon because it allows for deeper and more precise strategizing (a lot of things happen in-between turns, especially in late-game... slower game-play allows you to deal with fewer things in more turns, and kind of be more precise), and the main reason being that units don't obsolete as they are marching towards the enemy.