There is another use case where background applications would be handy apart from those already mentioned. When your phone goes into sleep mode (screen goes off and the phone locks, by default after 30 seconds) it suspends any running application apart from the iPod. For most applications this isn't a problem but there are some where being able to run whilst asleep is handy.
One such application is OSMTrack which is a GPS logger for OpenStreetMap, the application can prevent the phone from locking so it doesn't get suspended but it means leaving the screen turned on. Even at the lowest brightness the screen still kills the battery, this is the 'workaround' that developers have had to use as background support is not available. It also ties up the phone so you can't snap a picture or check an email whilst this app is running. I'm sure there are other applications like this.
As other people have said it's fine 99% of applications but there is the 1% where background support would be of a great benefit.
One such application is OSMTrack which is a GPS logger for OpenStreetMap, the application can prevent the phone from locking so it doesn't get suspended but it means leaving the screen turned on. Even at the lowest brightness the screen still kills the battery, this is the 'workaround' that developers have had to use as background support is not available. It also ties up the phone so you can't snap a picture or check an email whilst this app is running. I'm sure there are other applications like this.
As other people have said it's fine 99% of applications but there is the 1% where background support would be of a great benefit.