The embassy/consulate asks for proof of a round-trip flight reservation to ensure the applicant will not overstay their visa, and will get back to their home country before it expires.

Since a round-trip reservation shows the departure and arrival to your home country, this is a convincing document that you will return.

Most of the embassies and consulates in the world acknowledge the applicant’s loss of money in case of a visa rejection. Thus, they do not obligate visa applicants to book a flight ticket. For them, even holding the ticket works. The same is indicated in the list of required documents for a visa application by the authorities.

And once the visa is in place, the applicant can purchase the reserved ticket, or cancel and book another based on their convenience, within the time of the visa's validity.

No. You can have the Flight Itinerary for a Visa and get your visa processed. Later, when you have your visa, you can get the actual flights booked.

The only way you can get a Flight Itinerary for a Visa free of cost is by using a Flight Itinerary for a Visa generator. However, these tickets aren't held by the airlines and won't appear when the embassy/consulate searches for them online. In other words, these tickets don't have any live, valid PNR. In this case, a visa counsellor may reject your visa.

Yes, Flight itineraries for a Visa are legal. They are actually encouraged by embassies and consulates for visa processing.

While some airlines hold the reservation for up to 48 hours, most of the airlines hold the ticket for around 3 days.