Usually used when a student has to be registered for full-time status, e.g., to hold a teaching assistantship or fellowship. Take this after courses are finished, and before the preliminary oral exam. WRIT 8666 does not fulfill degree requirements and cannot be converted to thesis credits. You can register for this only twice; additional registration requires approval by your advisor and the DGS.
If you pass the preliminary oral exam early in fall or spring semester, you should switch your registration to WRIT 8888 Doctoral Thesis Credits by the tenth day of that semester. Register for 12 credits of WRIT 8888 for this and the following semester to satisfy the requirement for 24 thesis credits.