When surface associativity is on, surfaces are created with a relationship to the
surface or profiles that created them.

Associativity allows you to:

• Reshape the generating profiles to automatically reshape the surface.
• Work with a group of surfaces as if they were one object. Just as reshaping one face
  of a solid box adjusts the entire box, reshaping one surface or edge in a group of
  associated surfaces adjusts the entire group.
• Use geometric constraints on the 2D profiles of a surface.
• Assign mathematical expressions to derive properties of surfaces, such as height and
  radius. For example, specify that the height of an extruded surface be equal to one
  half the length of another object.

As you add and edit objects, all objects become related and create a chain of dependency.
Editing one object can affect all associated objects. It is important to understand
the chain of associativity because moving or deleting one of the links in the chain
can break the relationship between all the objects.

When associativity is on, the DELOBJ system variable is ignored. If Surface Associativity
and NURBS Creation are both on, surfaces are created as NURBS surfaces, not associative
surfaces.

Save time by planning your model ahead; you cannot go back and add associativity after
the model has been created. Also, be careful not to accidentally break associativity
by dragging objects away from the group.