What is the idea behind serving espresso with a lemon peel? I've seen espresso served with a lemon peel next to it, just wanted to know if there was a specific reason for this.  Theories I have:


Its flavor, specifically the oil that can be squeezed out, complements the flavor of espresso, although if this is the case I'd like to know why.  It would seem counter intuitive to me that you would want to add more acid to an acidic beverage, but I guess milk is slightly acidic too.
Its flavor covers up imperfections in bad coffee and/or poorly prepared espresso.
It is simply a garnish to make the presentation more appealing to the eye.


Maybe one more more of these contributes to serving espresso with a lemon peel?  Maybe something else?
This article states that it is possible it started in WW II when cafe's used lemons to clean their espresso cups due to the fact that water was scarce in Italy. And the "tradition" stuck and expanded.