So far at the moment, in both My Empire and Terra Nova, money doesn't really have important uses or relevant to important functions, other than keeping AI happy when they demand tribute (which is always roughly a 10% sum of your treasury last turn).
Players can always find themselves end up having hard cash piling up mountain-high in treasury that serves almost no purpose.
Demanding tribute from other AI/player is indirectly pointless for players.
Game over by bankruptcy (if there is) literally impossible.
Hence, to make things utilized reasonably, we should introduce other factors that would make money more important.
- Unit upkeep cost
In simplest manner, you'll have to keep your units paid if you want to keep them on field, every unit would cost upkeep, at the rate of 2 money per turn.
Considering you don't always have very immediate source of money at the start of the game, at most 3 units requires no upkeep at any given moment.
- Purchasing unit/building
AI tends to establish new settlements at sites with terribly low to nonexistent 🔨 yields which would severely hamper development and productions. This is when directly buying buildings can get handy.
Buying units can also be useful if you want to pump out one to two extra workers or as means of a desperate defense during wartime.
- Resource Trade / Trade Contracts
Since now we have buildings that requires resource in Terra Nova, we can start thinking about peaceful trade contracts between players or AIs, allow buying resources from other players or AIs using money.