For workers, flexibility is the key advantage of part-time jobs. Because they work less than a full-time day, they still have time to attend school, recover from an illness, care for family members, volunteer at worthy causes or work at another job for extra income. Those working less than half a day have the choice to work mornings, afternoons or evenings in establishments with longer hours. During busy periods, such as around the Christmas holidays at retailers, part-timers may be called upon to work longer or full-time shifts, which increase their earnings. A worker who shares his position with others in the same job knows that if he gets sick or needs to take a vacation, others can do his work.