Why Coins have Ridges

... dishonest people sought to make an illegal profit from these coins. They filed off the edges and sold them for their value in gold or silver. The smaller-sized coin often went unnoticed, but this dishonest practice decreased the value of the original gold or silver coin.

To prevent this, the government began milling, or grooving, the edges so a coin could easily be identified if it was trimmed.

That makes cents.