Yes, you can leave urban outdoor furniture on a balcony with no overhead cover, but only if the furniture is genuinely built for outdoor exposure and you're willing to maintain it. I've seen people do this for years with powder-coated aluminum and all-weather wicker, and it holds up pretty well. I've also seen cheaper pieces fall apart in one rainy season, so the material matters more than anything.
The tricky part of an uncovered balcony is that it's not just "outside." It's a small, exposed platform. Rain can blow in sideways, sun can hit for hours, and wind can push chairs around. In a city, you also get dust, exhaust film, bird droppings, and sometimes salt air if you're near the coast. That's a tougher combo than a covered patio.
If you want to leave furniture out, stick with materials that can take it: powder-coated aluminum, stainless steel hardware, teak or sealed acacia, HDPE, and high-quality all-weather resin wicker. Avoid untreated wood, mild steel, and anything with particle board. Cushions are the weak point. Even outdoor fabrics will fade and get mildewy if they stay wet. Bring them inside or store them in a waterproof deck box when you're not using them.
A good breathable cover helps, but don't wrap furniture in a plastic tarp. That traps moisture and can cause mold or rust. Elevate legs slightly so water doesn't sit around them, and make sure the balcony drains well. During storms or winter, I'd move lighter pieces inside if possible. Snow load can bend frames, and strong wind can send a chair over the rail.
Maintenance is simple but not optional. Rinse the furniture monthly, use mild soap for grime, dry it before covering, and tighten bolts once or twice a year. If you have teak, oil it when it starts looking dry. If you see a scratch on metal, touch it up to stop rust.
So the honest answer: yes, urban outdoor furniture can be left on a balcony with no overhead cover, but choose weather-resistant pieces, protect cushions, and expect some fading and wear. If the furniture is expensive or sentimental, cover it or bring it in. If it's tough, low-maintenance stuff, it can live out there just fine with a little care.