I stumbled across the term “hacksilver” on the History Blog the other day and decided to look into it, as I often do when I encounter unfamiliar words. It refers to silver items cut or bent into convenient sizes for use as currency, and it was apparently a common practice, especially among the Vikings, to use looted items of gold or silver this way.
I will absolutely have to remember to implement this in D&D. For one it makes more sense that vast piles of valuable metals are not minted coins at all.
I can see a tribe of goblins or kobolds accumulating a pile of coins a few at a time by stealing them from travelers and trading stolen livestock to orcs or whatever, and humanoids and humans would probably be very likely to make hacksilver out of their loot. Demihumans, who appreciate the aesthetics of crafted items, would not though.
And surely a dragon just carries off all the gold implements in a temple or palace before razing it, and keeps it intact; other monsters might collect shiny stuff from the ruins they haunt, including some coins but not a lot of those get left behind when a civilization falls (looting, hoarding, etc.).
Convenient coinage might appear in dungeons because the malevolent force that inhabits the underworld knows coins attract explorers to their doom, though, or because the dungeon inhabitants are actively minting coinage for their agents above-ground to use to bribe and buy from the civilized.
But most humanoids, bandits, raiders, and so on will have converted gold and silver items into hacksilver, either for dividing plunder or because they have no ability or interest in minting. You could just have a percentage die roll determine how much of the loot PCs find is in coinage (& hacksilver), and how much is in ingots and larger items for most monsters, but assume monsters with really vast hoards are probably collecting large items rather than coins (and certainly not bothering to make hacksilver).
I think this probably inverts the normal relationship between portability and treasures in D&D — usually, you think of items as being more ‘portable’ because a single finely-crafted item might be worth more than its weight in metal. So really the trade off should probably be that if you haul a golden platter, three feet across and worth 1000 gold pieces, back to town, no-one can afford to buy it from you, but if you hack it into gold pieces, you get 2/3 or 1/2 the value in hacksilver (well, hackgold) that can be readily spent. I kind of like the idea of an adventurer breaking an arm off of a silver candelabra to pay for his room and board, or pulling gold links off a chain necklace to by more oil and rope. Also, you might allow coins and hacksilver to be more portable (like 100 to a pound of encumbrance rather than 10), but the tradeoff again is that you would take extra time to hack the items up, or else need to make extra trips or be badly overburdened to bring all those plates, candlesticks, and so on out of the dungeon!