Some airlines require it explicitly and even charge "penalties" for non-compliance. If this does not work or is not available - for example on charter flights - many passengers get upset. We are talking about online check-in, which is now almost indispensable.
In the past it was generally customary and in most cases there was no other option: passengers had to come to the so-called check-in counter with their ticket, which was more like a small booklet, and their ID. There the boarding pass was handed over and the luggage checked in. Business travelers in particular, who in the "good old days" often only traveled with hand luggage, found it annoying to stand in queues and sometimes lose valuable time.
Some carriers have reacted to this and introduced what is known as telephone check-in. The data then had to be passed on, the boarding pass was then issued and initially deposited at a pick-up counter at the airport. Only a few carriers now offer telephone check-in, and if so only for frequent flyers with the highest status and/or first-class customers. Where possible, the boarding card will be sent by email or handed over to you by a member of staff at the airport.
The exact details and instructions for telephone check-in may vary by airline and airport. A dedicated phone number is usually provided for passengers to call to complete the check-in process. Irrespective of this: the telephone check-in was the precursor to today's internet check-in.
Alaska Airlines was the pioneer
Alaska Airlines was the first airline in the world to allow its passengers to check in online. From 1999, the US carrier gradually introduced this procedure. At first, only a few airports were equipped with barcode scanners, because boarding cards with magnetic strips on which the data was stored were still common at the time. In the meantime, these have been completely replaced by barcodes or QR codes, which helped web check-in to achieve a breakthrough and at the same time massively simplified the processes at both airlines and airports and made them more cost-effective. Airlines like British Airways and Lufthansa followed suit in 2000. Since then, however, the online check-in procedure has become widespread and is now available on most airlines worldwide.
The online check-in process offers passengers many benefits, including the ability to save time by printing their boarding passes in advance or saving them to their mobile devices, and the ability to select their seats in advance. It's also more convenient for travelers who only travel with carry-on luggage, since they don't have to queue in long queues at the check-in counter.
Low-cost airline Ryanair was by no means the first airline in Europe to offer internet check-in. However, the carrier quickly recognized the potential for cost savings and at one point even charged a fee for using web check-in. This could not be avoided, because this was simply added to the booking. Little by little, the low-cost company made web check-in compulsory and those who don’t comply or forget to take the printout with them (there is now an alternative smartphone app) will be asked to pay a lot at the airport. This practice is massively controversial, but has been copied by many other carriers. Even in the Lufthansa Group, there is a provider, Eurowings, who asks you to pay extra for the counter check-in in the basic fare. This is surprising because the predecessor Germanwings resisted online check-in for a long time and claimed in advertising newsletters at the time that customers would not want it at all, because they would appreciate the personal service at the counter. Just a few weeks later, web check-in was also available on many Germanwings routes.
With charter flights it is often very different
For package tours that include charter segments, it may happen that the personal check-in at the counter is the only option. However, it is not true that there is generally no internet check-in on charter flights. In fact, many charter airlines such as TUI fly, Condor or SunExpress offer online check-in for their passengers.
It is possible that some charter airlines may not have the necessary technology and infrastructure to handle online check-in. As a rule, however, many charter airlines also offer Internet check-in to make the travel process easier and faster for their passengers.
It should also be noted that some charter flights may have special check-in regulations due to airport or country restrictions. In such cases, the passengers may not be able to complete the online check-in, for example, due to the need to present certain documents or permits.
Overall, on many airlines, including charter airlines, Internet check-in is now a common and convenient way for passengers to register for their flight and receive their boarding passes.