Why do coins have ridges on the edge?

I am not sure how many people asked themselves this but I sure did.
Why do coins have ridges on the edge?
The answer is simple.
In ancient times the coins were made out of silver and gold.Especially gold.And they were flat.So many criminals back then used to file down the edges of the coins and collect the golden shavings.Then they would sell the shavings to make profit.Making money out of money,what a brilliant ideea.
But in 1792 the Coinage Act created the US Mint.
The Mint decided to make ridges on the edge of the coins so it would be harder for the thieves to shave them and for us to be easier to see if the coin has been "shaved" or not.
Nowadays coins are made out of steel but the ridges have remained because it is easier for the visual impaired to recognise the coins .