Actually my question was rhetorical. Perhaps it's a purely english expression, but it basically gives an example of what you are talking about. It's like another way of saying "That's what X is for" only in the form of a rhetorical question, usually pointing out the blindingly obvious.
To give another example, if someone said "I wish there was a way I could send these files to my friend in Venezuela.", one could reply "What's email for?". The question implies that the first person has overlooked email as a method, so it's kinda sarcastic in a way.
To give another example, if someone said "I wish there was a way I could send these files to my friend in Venezuela.", one could reply "What's email for?". The question implies that the first person has overlooked email as a method, so it's kinda sarcastic in a way.
