For most people anchovies are a love or hate ingredient. I have to admit that I love them! Like salt, anchovies are a natural flavour enhancer. They're rich in a compound called inosinate which, when combined with the glutamate you get in beef or lamb, emphasises the natural meatiness of those ingredients.
The very intelligent Romans knew this. Though the ancient Greeks probably invented garum, the liquor of salted anchovy (or mackerel) guts, dried in the sun, flavoured with herbs, decomposed by its own bacteria and then matured that became the chief condiment of Rome, seasoning almost every dish in the repertoire.