Persian, also known as Farsi, is used officially in Iran, Afghanistan, Tajikistan and by many people in Uzbekistan. Its influence was felt on many languages, including Arabic, Urdu, Zorastrian and Armenian amongst many others. Famous literary works of Rumi, Omar Khyyam, Ferdowsi and several others were written in Farsi during the middle ages.
Knowing the language enables you to communicate effortlessly with the locals, find jobs with ease and in a million small ways, it makes life so much more comfortable, fulfilling and interesting!