Given a travel related situation, and given a specific question about the situation, summarize the question into a title
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Question: I always thought that the point of "checking in" to a flight was so that the airline knew you were at the airport and would most likely board the plane. 

But nowadays you can check in by computer or smartphone, which is great -- but you can do so as much as 24 hours before the flight. That's before you even go to bed the night before the flight, let alone arrive at the airport.

If there's a emergency, or even very bad traffic, that makes you miss your flight, won't it be in the last few hours? What good is checking in so far in advance?

EDIT: And almost as soon as I finished typing my question, I saw this: What is the purpose of check-in before flying?


Answer: Why can you check in to a flight the previous day?


Question: I am specifically looking for the case in Indonesia. 

If a form is required, what sort of information is required on the form?

Or does this simply involve paying a fee and getting a stamp on my passport?


Answer: Does one need to fill in a form for a Visa On Arrival?


Question: My US child passport expires on December 4, 2016, and I'm planning on traveling in December.
I know I need a new child passport to travel then. 

However, I turn 16 in June 2017.
After I turn 16, would I still be able to travel on a child passport until it expires (around December 2021, I would be 20 years old) or would I need an adult passport then?


Answer:
Child passport validity