A set is a collection of objects or components. Any item you can select can be in a set. The set exists as a separate object representing the collection. Unlike groups, sets do not alter the hierarchy of the scene.
In some instances, Maya creates sets for you as you work with objects.
You can create a custom set so you can work on its items with a single action. For example, you can create a set of NURBS objects, then hide or display the set as a single entity.
You can control the membership of sets easily using the Relationship Editor.
Sets are useful for the following:
A partition is a collection of related sets. Partitions prevent the sets in them from having any overlapping members. Maya uses partitions to keep sets separate where overlapping members could cause problems.
You can create your own partitions when you want to create sets that have no overlap.