If you ship your bike somewhere, you prefer that it arrives there in good condition. This is a way to ensure that. Packing your bike in a box this way is a way to travel by plane without buying a specialty bike case or hard-bottom bike bag and still have your bike arrive undamaged.
When considering crank length for a mountain bike, it is important to keep in mind the type of riding that the bike will encounter as well as the rider’s morphology. The considerations for technical riding are different than for riding on smoother surfaces, and the length of the rider’s legs are also critical to crank length.