I am creating a custom theme. I want to use 2column-left layout for categories page. If I write something in local.xm it doesn't work at all. I feel it is of no use. but when for a specific category I select a layout e.g. 2columns-left it works perfectly.
Please check other xml files as well, this may be due to some module is overwriting the layout of catalog_category_view .
Magento starts rendering page as per XML file definition only and overwrites configuration based on custom settings added by user from Admin panel so check the setting of your theme and other xml files for right outcome. Definitely some xml file is overwriting the layout file which is again overwritten by your custom setting added in category section.