Folks want realism or immersion or a fantasy epic that deeply involves the players or escapism and yet over and over again folks want to keep the coinage simple. The bog standard is the familiar breakdown of 10 cp to 1 sp, 10 sp to 1 gp. pretty boring and non-evocative stuff.
If old school rpg is about discovery and escapism where are the Lemurian Shekels and the Goblin Empire's Lead Lupins? Why did the men of an ancient age mint coins in the same metals and denominations as commonly minted in a campaign's modern age?
I'm a victim and perpetrator of this myself while I've got foreign coins those of the campaign homeland are the plain old 10 cp to 1 so, 10 sp to 1 gp and 5gp to 1 pp coins. I do it for convenience but i feel i'm cheating the players a little as they have had no trouble keeping track of Trade Mission gold Tokens (gtk)or Hesparan Royales (GR) worth a base rate of 2/3 a gp or 2 gp. The coins are worth their relative value some of the time or are changed by a trip to the local money changer.
Now a trip to a money changer can be a trying experience. the money changer charges a small cut for his services and always downgrades the coinage to a lower denomination/metal. All foreign gold is returned as silver; if one wants gold coins there is another charge for buying all that gold. It is a mechanism to remove some cash from the players but it also pumps coin into the coffers of the local authorities... something for thieves to seek if they are daring enough.
One reason for the decimal accounting of our fantasy coins is encumbrance sometimes counted in overly large coins weights. Ive seldom seen folks really bother with counting all the coin weights and encumbrance gets hand-waved until everyone is caught walking about with 200-300 pounds of gold in their coin purses. I myself keep a simple 50 coins to a pound of encumbrance regardless of coin size themselves as encumbrance is also how bothersome keeping track of something is and 50 nickles really isn't much more or less troublesome than is 50 pennies so I live with it.
I'm starting up a new campaign soon and there isn't going to be simple decimal accounting of coins but I'll keep the coin metals in the names of the coins. I want escapism and immersion I want the players to feel like they aren't just shuffling about pennies, dimes and dollars. when one finds a stash of 40 Golden Lions they may realize those coins have been hidden away for a century and wonder what value there is in a clay pot full of Brass Minarum. beyond the treasure instantly disappearing into a nebulous cloud of coins that float on the character sheet lost among all the other faceless boring coins.