Through the tutorial quests you will several times be awarded
Gold Coins as a prize, and later on from defeating bandit leaders. You may or may not notice that these don't really help you out to begin with.
Once you've built your branch house, You may think to yourself: "Why not go ahead and use these useless coins to buy myself some swords or copper on the trade window?"
HOLD IT RIGHT THERE
Coins are possibly the
most valuable component of your economy, as they are required for many building upgrades (specifically
marble and
hardwood production infrastructure!) and explorer/general/geologist hires!
You will not be able to produce your own coins in a steady supply until you reach
level 23 and are capable of building a gold mine and a coinage, even at this stage they will not stockpile fast by any means.
Moral of the story: Do not part with your coins lightly!
100 coins for 100 bronze swords may sound fair at the beginning, but it does not take long to produce swords faster than you regenerate population.
Instead, wait to invest those coins in a marble mason upgrade and watch your resource production grow dramatically.