I feel that Piazza is efficient for the following reasons. Course communications are easily distributed and visible to all parties involved via the web. Questions answered by any one of the instructors (faculty or teaching assistants) are readily visible to all interested parties and can easily be amended by follow ups as necessary, thus eliminating redundancy and saving time. For a large lecture class, this cuts down on a lot of email.
I continue to be pleased with Piazza and the regular enhancements only improve my endorsement.
I love using Piazza for answering student questions; the user interface is unbelievably nicer than anything else I've seen. It is easy to enter text and easy to see what questions need answering; It is just easy to use.
Instructors can create a Piazza for their class with a single click.
Students and instructors are automatically enrolled with appropriate roles, based on the course roster.
When clicking on Piazza in Blackboard, users are automatically signed in to Piazza, so there's no need to remember a separate user name and password.