What's the point?: … (mà) làm gì

Làm gì at the end of a sentence, after an action, can mean "what's the point of …?". It isn't a real question: you're saying there's no need, usually to talk someone out of it. Mua nhiều mà làm gì? What's the point of buying so much? The voice falls at the end, and nobody is expected to answer.

Mà before làm gì makes the doubt clearer, and a reason often follows: Mua nhiều mà làm gì, ăn không hết đâu. A very common ending is cho mệt, "and only wear yourself out": Lo làm gì cho mệt. Why worry? It'll only tire you out.

Often it's kind, a way to comfort someone: Giận làm gì, chuyện qua rồi mà. Why stay angry? It's all over now. About someone else, it can sound weary: Nói với ảnh làm gì, ảnh có nghe đâu.

You've met (để) làm gì?, the real question about purpose: Em học tiếng Việt để làm gì? With để, you want an answer. Without it, the same words can be either, and the tone tells you which; mà or cho mệt make it clear you see no point.

Lo gì mà lo! also means "don't worry", but more briskly: it throws the word back. Làm gì có! at the start means "there's no such thing!"