If you're a novice porter then that advice will serve well & stop you doing anything stupid!Not in every case. What if the port is smoking fast and you want to slow it down? Wouldn't then the goal be to increase cross section with minimal flow gains? If the case above happened, wouldn't the port still be smoking fast?
But yeah, there are many reasons why you'd want a larger port even if the flow did not gain at the same rate as port volume - but those circumstances are a bit more advanced & you'll want to know what you're doing.