This website is such a useful tool for many reasons and should not be blocked. We do use it just for talking to each other (I can't speak for everyone, but my friends and I do NOT use it during class); we also use it for school-related purposes as well.
For example, I had a project in one of my classes, and two people in my group were without cell phones or home computers, so we used appear.in to work on the project. I used to go on appear.in frequently for "study sessions" with my friends and now I can no longer do this.
I understand that some people abuse the privilege of having a Chromebook and use appear.in during class, but people also go on many different websites to play games during class and these websites are not blocked.
I think a simpler solution other than just blocking appear.in, which others and myself use for academic purposes, could be this: When the teacher is not requiring us to use our Chromebooks for the lesson, they can simply ask us to close our Chromebooks. This is what my WHAP teacher does and the problem of students misusing their Chromebooks vanishes. My math teacher also has everyone keep our Chromebooks closed at all times unless we specifically need them for the lesson.
Hopefully this can be reviewed and thought about by the schools who have blocked this website.