what is the point of dubloons?

[Bogdan.]

it isn't really clear to me what i should use them for, the game tells me to keep them in chests; why?

why not just sell them to vendors as you get them, and what chests should i keep them in?

[ad5ian]

There's no need to keep them in chests. Just store them on your ship chest. In some treasures you will find chests of 150 doubloons each, also empty chests that can be filled with doubloons. There will be a need for doubloons in some quests, but the thing is doubloons are connected with the age of piracy in the Caribbean, so they give a better feeling of the era. Also when you hoard them in large quantities, you really feel like a pirate that gathered mounds of gold coins.
If you search google image for doubloons, you can see how cool they are and how must have been to capture a ship with coffers filled with doubloons.Also the Spanish gold ingots from that time looked very cool (also google image for Spanish gold ingots) unlike how they look today or how are depicted in the game both the doubloons in the inventory and the gold and silver ingots. The three sizes of bags of doubloons that you can find when boarding ships look very cool, though.

[Bogdan.]

so they look cool, that is it?

[ad5ian]

To me yes, because i didn't need to exchange them. In the game, doubloons are needed in several quests. Also if you have problems with any nation, you could pay Fadey or that priest in Martinique to settle things and they only accept doubloons. Later you will have access to a lawyer in Port Royal that accept pesos. Buying goods of strategic value (like ship silk, ironwood, ropes and resin used to improve ships, and the large ships requires a lot) can be made only for doubloons and only if you have the right connections. Those goods are very expensive, like 30 doubloons a piece of ironwood. Also for improving a ship at the shipyards in the capitals, the masters accept only doubloons.
Also buying a trading license from the Dutch West India Company in Willemstad, needed to legally enter the Spanish cities, can be made only for doubloons.For 20 days (minimum) the cost is 308 doubloons, for 180 days (maximum) the cost is 938 doubloons.That license is easy to lose if you attack another ship (excepting pirates) so it is better to buy the license for short terms although is not as cost effective as the maximum one.
To me, a successful pirate is the one that amasses a huge treasure. :) A goal for the game can be to gather like 1.000.000 doubloons, not pesos. :)

PS Of course if you are in need of pesos to pay your crew or to buy a ship, you can always exchange you doubloons at the banker for pesos.

http://blog.greatamericancoincompany.com/tag/what-are-doubloons/

http://i.telegraph.co.uk/multimedia/archive/03413/_1_3413012b.jpg