Everyone used whatever currency was locally availible, with every merchant in border regions being very aware of conversion rates. Throughout history there was also a cronic shortage of smaller-denomination cash, stuff for normal people to buy normal things. Today, we see "clipped" coins as evidence of forgery when in fact much of that was likely related to a lack of loose change. Nobody in town able to break a gold crown? Well, maybe you buy a horse with a slice of gold from that crown.
Clipping and dissecting a coin into smaller pieces for down-conversion are very different things. The piece of eight wasn't haphazardly cut, but instead pre-indented for breaking cleanly.
If you want to buy something worth 6% of a gold coin, whacking off an edge of one is a weird way to do it. You'd need a scale handy.
