i use them to get harvests. if you have a battle coming up, and it looks like you are vastly outnumbered, put all your houses to production and pay 2 bucks and use them do a few dozen harvests to get more production, build a big army in a small amount of time and go and win.
also look at the market. if you see that farms are selling for much much higher than usual, then put all of your houses to farms and spend civbucks on harvests and sell on the market to make coins,
or if you want some gold to buy a great person when you see a great person drop in price and dont have coin to go get it.