Once i was thinking that DocumnetSet is same as a folder in SharePoint. So i did some readings and found this.
“There is a difference between a folder in SharePoint and a folder on your desktop. Microsoft made them look the same in the GUI to make it easier on users, but that’s where it stops. In SharePoint, a folder is simply a “view”. In other words, it is a way to limit the number of items the database displays. If you look at the URL, it’s a long complicated way of saying only show me the stuff assigned to this naming designation.
So if folders are views in SharePoint, why can’t I change them like views? You got me there. Somewhere along the line, the capabilities of the “folder” view and the “normal” view diverged and different rules applied. For example, I can add unique permissions to folders, but I can’t add column properties. The opposite is true for views.”
The point is in SharePoint 2010, Microsoft decided to change how it thought about Content Management. Since content types have caught on as the best way to solve the problem of “a single set of rules and naming conventions,” they started to think how they could exploit that scenario to group things together. THUS, the document set.
A document set is a group of related documents that can be created in one step and then managed as a single entity. A document set is not a view, but a special content type. It is managed and deployed from a site collection level. You can create custom document set content types with site columns and managed metadata. You can apply unique permissions to document sets. You can view a document set’s version history. You can trigger workflows within a document set.”