A through ticket puts both flights to Bali on one booking; separate tickets are two unrelated bookings that happen to meet at a hub. For a first trip, our advice is the through ticket. Separate tickets can cost less, and they move the risk of a missed connection and a stranded bag from the airline's booking to you.
What the two options are
A through ticket is a single booking that covers the whole journey from your US airport to Bali, with a connection on the way. Separate tickets are two bookings: one from the United States to a hub such as Singapore or Tokyo, and a second, bought independently, from that hub to Bali. No US airline flies to Bali nonstop, so one of the two applies to every traveler.
Why people split the ticket
The reason to buy separate tickets is price. A long-haul sale fare to an Asian hub combined with a regional flight into Bali can come to less than a single through fare. We quote no figures, because fares change daily. The saving is real on some dates and absent on others.
What a connection is, officially
The US Department of Transportation describes a connection as a change of planes, nearly always with a separate flight number for each flight. Its consumer guide ranks a connection between two different airlines as the least secure arrangement for checked bags, behind a nonstop, a through flight, and a connection on one airline.
What changes when a flight is late
A late first flight is where the two kinds of ticket differ. The Department of Transportation's advice for any connection is to ask yourself what will happen if the first flight is delayed, and to pick another flight or build a longer connection if you do not like the answer. With two separate bookings, that question has two airlines to answer it.
Ask before you buy
We have no official source on how any particular airline treats a passenger who misses a separately booked flight because another airline's flight was late, so we will not describe it as a rule. Our advice is to ask the second airline directly, before buying, what its policy is for a passenger who does not reach the gate in time.
What the law offers
The Department of Transportation notes that on international itineraries passengers may be able to recover expenses resulting from a delayed or canceled flight under Article 19 of the Montreal Convention, by filing a claim with the airline. That is a claim made afterward, with receipts. It is not a seat on the next flight.
Bags
Checked baggage is the practical test of a ticket. The Department of Transportation advises that if you have a connection involving two airlines, you should ask whether your bags will be transferred. On two separate bookings, plan on the possibility that the answer is no, which means collecting the bag at the hub and checking it in again.
What collecting a bag involves
Collecting a checked bag at a hub usually means passing through that country's immigration and customs, then checking in for the second flight as a new passenger. You are then entering the layover country, and its entry rules apply to your passport. Check the State Department's page for that country before you book this way.
Carry-on only
Traveling with carry-on bags only removes the baggage question from a split itinerary. It does not remove the missed-flight question. Check the cabin allowance of the second airline as well as the first, since the two may differ.
