Technically what does "Checking In" really do?
 

It seems so basic. To "check in" for a flight. But what does this actually do on the American side? By initiating this action, does this limit any other types of actions? For instance, I want to standby for an earlier flight. I requested the standby but do I still "check in" for the original flight? By initiating check in what does this guarantee?

It also changes the e-ticket status to 'CHECKED IN'. This means e-ticket cannot be exchanged (reissued) for a new itinerary without changing the status back back to 'OK FOR USE'.

The only real reason you need to check in is to get a boarding pass, if you don't want to stop at the kiosk at the airport.

It doesn't foreclose anything else.

Well, I guess that just before they close the door, they might call your name in the boarding area if you show as checked in.

It may not "foreclose" anything else, but if you're not checked in 45 minutes prior to boarding (or 60 minutes for international flights), you may be foreclosed from getting on the flight.

Generally speaking it's a good idea to check in online if you think there's any chance you might run late (but still make it to the gate in time to board).

I can't think of any disadvantage to checking in. You can still do things like same-day change and seat change after you have checked in.

On the other hand, if you do NOT check in by the appropriate check-in deadline, you will not be able to board. Your seat will be given to a standby passenger.

For a standard domestic flight, check-in by T-45 as required assures AA that a passenger is likely to show up at the gate no later than T-15 when the passenger is subject to off-loading if he does not show.

There is no passenger downside to checking in as soon after T-24 as possible. The fact the changes may require a reissue is of no passenger consequence.

Interesting. I thought after you check in that same day change is not longer available online, and have to call in to uncheck in before you could change flights?

Someone can correct me please, but I was under the assumption that when the airline has to offload a passenger, check in time is used to determine who will be selected.

It depends on the policy set out by each airline. But yes some, if not all airlines, do use time of check in when determining which passenger to offload in an oversell situation.

Although I think there are some other considerations. For example a family traveling together where they won't off load a parent. Its probably why sole travelers get the toss (as in the Doctor on UA Express.)

I seem to recall that when travelling on a Gov ticket, up to the point I checked in, CWTSato could cancel/change/refund etc... but after that I'd have to work through the airline unless I un-checked in. Minor point, but makes a difference if my operations change.

US law requires that each carrier publish its IDB policy. Check-in time is certainly a valid choice, but class of service, elite status, fare basis and time of booking, are also factors. Often, status is the first criterion.

To a certain extent, it seems outdated and with a purpose that has passed. Delta automatically checks people in ...

Of course, the new air travel bill will prevent airlines from deboarding people who have boarded when the flight is oversold.

I also remember when it was not possible to change seats online after checking in. I now see this is possible.

IME airlines rarely ever bump someone already on board. I've had an announcement made asking for volunteers during boarding. A couple years ago I was sitting in 1A and the GA came on after boarding and asked for a volunteer ($500 voucher). I jumped up and volunteered. He told me to gather my belongings and he'd meet me at the podium. After about 15-20 minutes he finally comes back to the podium and tells me to go ahead and reboard.

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So if you check in for a flight from xxx-yyy, and that flight is delayed for 3 hours, and there are empty seats on the next flight from xxx-yyy that will now leave before the flight you checked in for, you're not at a disadvantage of getting rebooked on the later (now earlier) flight compared to someone who hasn't checked in? All other things (status, fare paid etc) being equal? It seems like it'd be easier/path of least resistance to put a non checked-in passenger on a different flight than one who has checked in. In any event I feel fairly sure there have been at least a couple of instances where I felt fortunate to not have checked in early, that my situation was better than if I had checked in, though I may be mistaken. I think the overwhelming majority of times it is beneficial to check in as soon as you can, but "no passenger downside" at all? Ever?

I thought checking in was a more formal - and since 2001, perhaps a more regulated - procedure that replaced the old reconfirmation (call the airline 24 to 48 hours before departure, reconfirming your reservation). Back then tickets were essentially transferrable coupons, so passenger names and individual data were less important than head count.

But Dr Dao was travelling with his wife, (who supposedly agreed to deplane)
https://en.wikipedia.org/wiki/United..._3411_incident

I think this is it. It also serves as a reminder for people the day before the flight to ensure that everything is good relating to their travel plans.

Thats my point.

No PSS (passenger service system) I have ever used at an airline would require extra or more complicated steps to move a check in versus non checked in passenger in the scenario you described. So no downside to being checked in.

Thank you OP for asking, as it is something that I don't really understand either. If airlines will have an option to automatically check you in, (which seems far from uncommon these days) what is the point of it in the first place? Why does it need to be a different function from purchasing the ticket/reservation? Especially considering earliest check-in times can range from 2 hours (when you have to check in at airport) to 60 days, at that point, what is the purpose of it as an additional step?

Somewhat related - Failure to check-in and pull up your mobile boarding pass prior to boarding beginning could make it impossible to get on the flight, which is relevant if you are cutting it close. https://www.washingtonpost.com/news/...=.53d10dc2aa29