Some tequilas still pack quite the punch, and salt and lime can help mask the intense burn. When you lick straight salt, it can distract your taste buds from the intensity of the alcohol that is soon to follow. Sucking on an acidic wedge of fresh lime immediately afterwards acts as a chaser, and can alleviate that bite while enhancing the pleasant citrus notes present in tequila. This ritual makes the whole experience less intense (and therefore makes it more likely that you'll do it again).

Source: Yahoo!