Request a Duplicate Passport If You Travel Internationally Often
If you want to see the world, you need a passport. If you want to see the world with a little more security and ease, you could use a duplicate passport. 
The reasons you might want to apply for a duplicate passport. These include traveling internationally while you’re applying for a visa in another country (since you’d have to submit your passport book for visa processing) and avoid questioning from Customs when you’re travelling between politically sensitive countries.
For most travelers, the biggest benefit of having a duplicate passport is so you can keep traveling even if your other passport is lost or stolen:
One common fear of frequent travelers is having a passport lost or stolen abroad. While applying for an emergency passport replacement is possible, the process can be difficult and unpleasant to begin with. Furthermore, an emergency passport is only valid to return to a home country - requiring the traveler to apply for a new passport prior to their next travel.
By holding a second passport book, travelers can maintain their international travel plans even if a passport is lost or stolen abroad. Through holding a duplicate passport, travelers will still need to report their passport as lost or stolen to local authorities and the State Department, but can still travel while they wait for a permanent replacement to arrive.
So if you’re planning a multi-country trip, you can consider a duplicate passport a kind of travel insurance.