when two things are accomplished with the effort for one this phrase is used to convey the same and sound intelligent.. it's usually a self-pat on the back situation.
See how clever I am, I brought Parvati from the village to get her a job and am paying only Rs.1000. Now she not only cleans the house, she also cooks!! One stone, two mangoes! how? nice no?
Added 2011-09-10 by sykil