The left and right sides of a sofa are typically designed to accommodate different seating preferences and body shapes. The left side is often considered the primary seating area, as it aligns with the natural position of the human body when sitting. This side is usually wider and more comfortable for extended periods of sitting. The right side, while still functional, may be slightly narrower and less accommodating for taller individuals or those who prefer a more compact seating arrangement.

This design is based on ergonomic principles and market research. According to a study by the American Home Furnishings Alliance, the average sofa is used for approximately 2.5 hours per day, with the left side being the preferred seating area for most users. Additionally, a survey conducted by the National Sleep Foundation found that people tend to sleep on the left side of the bed, which suggests a natural preference for the left side in seating arrangements as well.

The left side of a sofa is also strategically positioned to provide easier access to armrests and cup holders, enhancing the overall comfort and convenience of the seating experience. This design consideration is particularly important in the United States, where comfort and functionality are highly valued in home furnishings. The preference for the left side of the sofa is further supported by the fact that it aligns with the dominant hand of the majority of the population, making it easier to reach for items or adjust the position of the sofa.