If you book your own international flights, you risk not knowing the travel document rules of countries to which you are traveling -- or even in which you are changing planes. If you have failed to abide ahead of time, you may face an exceptionally long wait or even get sent home -- at your expense. Some countries will not let you in if your passport expires in less than six months, others will not admit you if you don't have a specified number of blank passport pages, and there are other arcane rules that are difficult to know.
For example, travel Guru Christopher Elliott, in his Elliott's Daily Report email, recently told of a traveler flying to Asia from Seattle, with a connection in Canada (many divers do this because of better fares on such airlines as Air Canada and Cathay Pacific). When he arrived at the Seattle airport, he was told that because his flight stopped in Vancouver, he needed an Electronic Travel Authorization (ETA). Because he had not done this ahead of time, the Air Canada agent had to handle it, but it took so long that he missed his first flight.
Knowing that if he canceled his next flight from Vancouver, he would be able to recoup some of the cost, so he emailed Air Canada to cancel. But that's not an instantaneous way to cancel, and he was declared a no show and lost all that he paid. To avoid problems such as not knowing Canada's ETA rules or Indonesia's U.S. passport rules or scores of other document issues, there is a solution.
The website http://www.iatatravelcentre.com allows you to enter your trip details and determine your documentation requirements.
You can also get documentation information from the U.S. State Department at this site: https://travel.state.gov/content/travel/en.html
While a savvy travel agent will clue you into the requirements, if you insist on planning your own trips, these sites can save you from a disaster.