To pack dirt: You put all your waste, nylon, bottles, food waste inside, then cover it.
For RIWAMA / Waste Collectors: When the waste truck comes, they will just roll it out because it has tyres. You don't need to carry it.
To keep environment clean: It stops rats, flies, and smell from spreading because it has a tight cover.
For separation: Green is mostly for general waste. Sometimes estates use different colors - green, black, blue