The reason that you would wait is so that the springs settle. They will compress down slightly from the installed height when new in about 500 miles. They should stay that height until the start to wear out. That's why people wait for about a week. All springs do this to an extent.
Also, word of advice. The factory aligns the vehicles from the factory, but the car gets tied down several times during transportation and this compresses the springs. Most of the time the alignment will suffer due to this. Not a bad idea to get the car aligned within 1500 miles of purchasing the car. Go to the dealer and complain of pulling or that the car tends to try to follow pavement grooves. Warranties vary, but most allow for a warranty alignment on a complaint basis within the first 1500-2000 miles of purchase. Some are longer. You have to complain though. If the ride height changes from the factory settings, the toe will be off and cause wear. It's free if you bother the dealer about it. Check your warranty for the actual mileage for adjusment. The dealers usually don't mind doing warranty alignments since it pays them nearly the same time as customer pay work does.