Text editors

If your students and teachers need only plain text or if they can use html it's ok to disable editor from all users from site administration.

If some of them need plugins http://docs.moodle.org/en/HTML_editor for inserting images, tables, links, smileys, changing fonts, alignment or colors etc don't disable editor site wide - tell students how to do it from their Profile themselves.

The behaviour you explained in previous post is not normal if students just write text, maybe you should check first where exactly did that student have those freezing problems. Is the main problem in non functional spell checker? What happened? The reason is sometimes in extra (browser) plugins or malware, network connection, office programs (if you paste long texts that may have macros, event handlers or scripts "hidden"), keyboard itself or sometimes students can do odd things themselves without any logical explanation.