What I understand is that platform length is related to a limited of goods or passengers. A 160 m platform has a limit of 160, a 240m of 240 and a 320m of 320 goods or passengers. And what I understand (but pls confirm!) is that the only thing which makes the difference between platform lengths.
No penalty/problems with long trains and small platforms (or even no stops), no possibilty to use (longer) platforms for multiple (small) trains at the same time, etc. But maybe I am missing something here?