You know, just so that everyone is sure it can do what it says on the tin.
The Koenigsegg brand is all about pushing the limits of what is technically possible and the Regera is a perfect example of this endeavor. It's got an incredible transmission with no gears and can do incredible acceleration and deceleration runs. As you can imagine from a car capable of a top speed of 250 mph, reaching 186 mph is absolutely effortless. While Segg fans will be well aware of these abilities, they might not have known that the Regera's quality control processes include taking every example from rest to 186 mph and back again.
The Koenigsegg Regera is a pretty revolutionary vehicle, so it's important for Koenigsegg to test every car to ensure that it is capable of the brand's claims. And with the Regera being a record-holder, nobody wants to hear stories about the Regera being tested by a customer (as unlikely as that is) only for said owner to be disappointed by its real-world abilities. Koenigsegg is also a small company, and much of the production of its astonishing vehicles is overseen by humans, not machines. Thus, there's always the possibility of human error creeping in, and Koenigsegg wouldn't want to increase the chances of a crash by delivering a vehicle that can't withstand high-speed runs.
Another point to make here is that only 80 examples of the Regera will ever be made, and as a limited-edition machine, it would be a travesty if such a car were to suffer some sort of failure under high-stress conditions. This makes the Regera one of very few vehicles in the world that owners would be pleased to hear had been taken for a joyride. It's a pity that most of these cars will be kept in climate-controlled garages and rarely - if ever - taken to the limit, but at least every single one has tasted 186 mph before its owners sell them on for stupid money.