In my experience, 0.5A chargers (and PC USB ports) are functionally useless for charging many modern smartphones and tablets, especially after a deep discharge. There has been many times I've put on a device to charge on a 0.5A source and come back to find its battery completely depleted. The charging will fail to keep up with the device's idle energy consumption.
If your device uses more than 0.5A for idle energy consumption, your phone's 1500mAh battery would only last 3 hours. Standby time on most smartphones is usually at least 12 hours, consuming between 100-200mA. Being able to turn the device off, and charge for 3 hours while cooking dinner and hanging out around the campfire is awesome.
