What does always-on mobile data do?

[djqwikcut]

I dont think I want to turn this off.. If Streaming audio shuts off after 5 minutes then thats no good.. I listen to a LOT of streaming audio.. I also dont want it to break the weather updates that I read in this thread it does.. and who knows what else.. I want the phone to get updates when it is supposed to.. There is no point in a smart phone if I have to turn off the updates and manually do everything....