ECJ - Yep. Just wanted folks to know and have a reference for when it is
required.
WCJ - I agree. It's a good practice for any depth of ceiling joist if you want to keep your ceiling looking nice.
To All - note that if the attic space will be used for storage, then the floor framing requirements for lateral restraint need to be met. This does not depend on joist depth.
§R502.7 Lateral restraint at supports. Joists shall be supported laterally at the ends by full-depth solid blocking not less than 2 inches (51 mm) nominal in thickness; or by attachment to a header, band, or rim joist, or to an adjoining stud; or shall be otherwise provided with lateral support to prevent rotation.