Although boarding back-to-front is mathematically more efficient, airlines typically board front-to-back or by groups primarily for commercial and loyalty reasons. By boarding premium cabins (First and Business) and elite frequent flyers first, airlines provide a tangible "perk" to high-paying customers, allowing them to settle in, enjoy a pre-departure drink, and—most importantly—secure limited overhead bin space. Additionally, front-loading helps ground crews ensure that the most valuable passengers are on board quickly, which minimizes the risk of a late departure for the aircraft's high-yield segments. Some airlines also use this method to manage the aircraft's center of gravity; loading the front can prevent "tail tipping" on larger planes where too much weight in the rear could cause the nose to rise while parked at the gate.