Another example is if your using it for something like VoIP.
If you want to be able to do voicemail, conferences, transfer phones, put people on hold, work with multiple protocols, hook into a T1 or POTS and all that then your VoIP system is going to require a backend that can handle manipulating audio and transcoding between different formats.
Sure most of the audio formats used in VoIP are uncomplicated, to say the least, but if your handling a call center with a 100 phones with the multiple voice bridges and all that stuff then it adds up pretty quick.
Then another issue is the sound cards itself. Sounds cards only support certain audio formats and your going to have to be able to support a multitude if your going have a efficient way of outputting to the real world.