Actually there is a scientific reason that chefs are taught to use lemon juice on their meats. Amines (which are found in proteins) have a chemical formula R-NH2...they are volitile and if left out long enough (doesn't have to be long at all) the meat starts to smell.
But if you add a hydrogen proton (H+ from the lemon juice) it reacts with the NH2 to form R-NH3, which is actually a salt and is not volitile, thus no smell.
If there's a bad smell, are you gonna wanna eat the food? No, that's why they add lemon juice. To keep customers.