The reason for the stringent checking is two fold. Obviously, no mint wants to issue currency that has some form of error in it's manufacture, but secondly, currency—especially coins—that have errors are deemed highly collectable and can be worth a lot more than face value. Again, not something a mint wants to have happen to their currency.
Thus, in 2008, Chile was subjected to global humiliation by the discovery that they had minted a number of 50 pesos coins with the name of their country misspelled. They were quick to fire the head of the mint and a number of his colleagues for the mistake.
Debates still rage today as to whether the error was a mistake or done on purpose to produce a small selection of highly collectable flawed coins. The mistake was the spelling of Chile with an "I" in place of the "L", making the mistake very difficult to pick up.
While most believe this to have been an honest mistake, nobody will ever really know the truth, but suffice it to say, the flawed 50 pesos coins are worth a lot more than 50 pesos today.
