The thing is, you don't actually care that much about your "gold stockpile", mostly you ensure that there is not a net loss.
In the Total Annihilation/Supreme Commander games, it's more like a regular RTS resource: you use it up, until you have none left, then wait for it to trickle/fill up depending on how many extractors you have. Since you're not always building, your stores just fill to capacity, until such time that you need to produce more stuff, where it becomes empty again. So you can really build in bursts, at the end of which building becomes a crawl, then you have to "rest" (well except in SC which at some points felt more like a reverse Tower Defense game, with an automated, endless trickle of troops from your factories into the enemy and viceversa). The only difference with Warcraft is that the mine/forest never runs out.
In Kohan, regular buildings (not necessarily mines) give resources and unlock troop types. So, if you're going to have a mage-intensive army, you have to make sure that you have enough magic resources produced at any given time, and so on. If it's going negative at all, you're doing something wrong and you need to correct it. Gold is simply a buffer telling you how much time you have to fix the problem before it starts having consequences.
Don't remember other uses for the gold. Maybe some things you had to purchase, not sure. Blacksmith upgrades maybe.