User blog comment:Kirkburn/Technical Update: September 2, 2015/@comment-5973717-20150904162145/@comment-126761-20150904173019

The main rationale is as a security checkpoint: as part of our security review we are not only looking at how to fix existing concerns but also improve them going forward. Personal JS is such a powerful feature, it makes sense to double-check someone actually understands it. While it might be an obvious choice for many that check these tech update posts, many others may not understand the full implications of it - so benefit from a simple checkpoint.