I cannot speak for OP's ? but my impetus for non-alpha is separating words. I do not like underscores, so I use hyphens and spaces where they work, for tags, todo keywords, and properties. I think search doesn't allow escaping - yet, but otherwise they seem to work for my purposes. I do not recommend this, but it's useful.
-- The Kafka Pandemic: http://thekafkapandemic.blogspot.com
