Ok so its not that useful perhaps, but it can save some time (not having to trade an enchanter and asking them to disenchant)
Basicly before you go out (or into an instance) to farm, ask an enchanter friend of yours that is anyway just leeching a city, doing bgs or doing other single player content to join your group. If you have an enchanter in your group, no matter how far away he is or what he is doing, the disenchant feature of the rolling will be enabled. So basicly you can just disenchant every item dropping by a simple keypress instead of going to a city and begging some nice soul to disenchant them for you.
This can also be very useful if you are farming bosses in old instances or something for Large Brilliant Shard, or similar.
(Perfect for strat runs etc, I'm not sure how profitable they still are, but they used to give pretty good gold by disenchanting everything!)
It might be common sense to some, but I do not think this is what blizzard intended when they added the feature.