Custom post types benefit from having meta boxes - so why shouldn't devlopers be able to extend taxonomies with meta boxes as well?
This will give the ability for me to create a custom post type, and have it sorted by taxonomy, and have each taxonomy add meta data to the post types, based on their classification in the taxonomy.
Take a look at this example: http://net.tutsplus.com/tutorials/wordpress/introducing-wordpress-3-custom-taxonomies/
And imagine that you wanted to add a featured image to the PC taxonomy, allowing meta boxes to be registered for custom taxonomies would enable this functionality.
Overview
- Provide a hook for developers to add meta information to custom taxonomies, consistent with custom post types
- Provide an
update_taxonomy_meta($taxonomy_id, $key, $value)function to manage the data.
Zeb 
