This is part of the point I was trying to make in my original post. I just don't see the point. If you are following proper quarantine procedures pre-treating new additions/snakes coming back from a show shouldn't be necessary. If mites show up during the quarantine period treat them. The risk of cross contamination should be pretty low if you really are quarantining.
That said my original intent for this thread was about people who use mite spray on a regular basis when they don't have mites. I've seen a few people post that they treat the substrate every time they put new in, and some who treat every few months. I just don't understand that mindset.