Why do some coins have holes in them?
In some cultures it used to be common practice to sting coins together to use them at a higher denomination.
Someone for example could string ten 10c coins together to make one unit of their currency. Keeping them together like this makes them easier to use and keep track of.
George III Shillings do not have holes in them. The hole may have been bored, not at the mint, but by someone wanting to keep it with other coins on a string around the neck. I have some old British coins with holes, obviously not part of the original design. Any modification to a coin is very possibly illegal and makes the coin valueless as a collectible.