Jessica,I basically agree with Steve.My college is part of a consortium of all community colleges across the state. Our online students can and often do take courses with other colleges in the consortium, so there's no possible way we would ever allow students to enroll or unenroll themselves in a credit bearing course. In public institutions where the students receive national funding (PELL Grants), we have to carefully track attendance. At each college, the eLearning staff work in coordination with our Registrar and the IT for our native students, and then the Virtual Community College staff at the state level manage the online classes. We have to complete audits, and students dropping, adding, and changing sections would be a nightmare, especially for naive freshmen.
Trying to think of how/when/why you would have a Canvas participant enroll/unenroll in a course, I could see that for staff development and/or training in a Canvas course set up for just that purpose. For students - possibly, and I am really trying to think outside the box, student social groups such as intermural sports?
It's a great question, BTW, and definitely something I had never considered.