I think it depends on the baby to be honest. Mine would have been a waste of money as my DD will quite happily sit in her bouncer for hours watching me go about housework, making phonecalls etc, but I know I'm lucky, other Mum's find them a godsend. Some babies use a swing to get to sleep for naps or to relieve colic symptoms I think etc.
Its also a big bit of plastic cluttering up your house (I don't have a swing or a jumperoo or a walker but took 10 bags of stuff to the charity shop today to make room for DD's mountain of STUFF) - so make sure you have room for it and can store it when you've finished using it for good.
Valentine Xxx