Last modified: 2008-06-26 00:27:22 UTC
Currently main.css and commonPrint.css currently contain definitions for a CSS class called townbox. This was introduced somewhere in 2004, in preparation for a new "Infobox" for cities in the german wikipedia it seems (http://de.wikipedia.org/wiki/Wikipedia:Archiv/TownBox).
Anyway, it seems it never really caught on, and as far as I am aware, not one of the wikipedia sites is using it. Besides this, I do not think this is CSS that should be part of monobook/main.css or commonPrint.css This box was not part of the MediaWiki software as far as I know, and as such I believe this markup needs to be removed. Besides, it's monobook only.
Thus many reasons to remove, few to none to keep :D
It was introduced in commonPrint.css here, not sure where the main.css is:
Removed in r36662