The answer depends heavily on the material. High-quality all-weather wicker, powder-coated aluminum, teak, and certain treated metals are designed for permanent outdoor placement. However, "all-weather" does not mean "maintenance-free." Even durable materials benefit from protection.
For long-term durability, covering furniture is strongly recommended during harsh weather, especially winter. Covers shield against UV rays, which cause fading, and prevent moisture buildup, mold, and debris accumulation. For cushions, storing them indoors is essential.
To decide, check the manufacturer's specifications. Use furniture covers for extended harsh seasons, clean regularly, and consider your local climate. With proper care, your urban outdoor furniture can be a lasting year-round feature.