Early coinage was made of
silver and it wasn't until 1697 that milled coins were seen in general
use, before then coins were handmade and stamped.
The reason for milled coins being introduced was to stop the illegal practice of 'clipping'. Clipping involved cutting small slivers from the edges of coins. Once
a sizeable hoard of clippings had been collected they were either
melted down and turned in to new handmade coins or since this offence
was punishable by death, sometimes sold to silversmiths.
In the photo below it is clear to see from the flat edges on the coin that it has been 'clipped'.