There’s a Terra Nova thread titled Source Identification and Soulbinding which basically says,
…soulbinding is a “source identifier.” In WoW-like systems, you know if a person has been through a particular dungeon because the item they’re carrying could only have come from there. I have a Misplaced Server Arm, thus, you know I’ve been in Naxxramas. Fine.
But in DDO (which does have soulbinding, but to a lesser degree), the difficulty is that I can’t read the life story of a potential groupmate in their equipment.