I am not absolutely sure that this was never done in any other game before, but to me it’s an innovation. In SoD, you can gain experience while offline, or while in an antirely different place than your friends, or while shopping at vendors.
This works through Adventuring Bands. You invite the people you like, and if they accept, the exp they gain is shared between all members of the band. The thing I like most about this is offline exp. My girlfriend has a bit more time to play than I at the moment, so we just form an adventuring band so that Ayba and Oric’s levels don’t go too far apart. So look what happened when I logged on Oric today:
You can use this in other ways as well, for example to keep the exp flowing while one of the group members has to run off to the vendor.
An extremely nice feature that I’d love to see in other games as well.