What are combined shells and how might I use them?

Combined shells are populated with students from two or more sections of the same class, e.g., COM110-82 and COM110-83.  Shells can be combined in either the Blackboard or Moodle LMS.

What are the advantages and challenges of using combined shells?

How do I combine my shells if I decide to do so?

How are combined shell availability and enrollment handled?