'Swapped out' is to my knowledge a computing term where it makes some sense (swap file, here) but I can't see its usefulness in general terms. e.g. 'I swapped out my old laces for some new ones'. Why 'swapped out', why not just say 'swapped'? e.g. 'I swapped my old laces for some new ones.' What is the function of the word 'out' in the first example? A rather trivial issue to be fair but was just wondering as I see the term used here quite often (think it's more of an American English thing but I'm not sure).