You need to add define('WP_ENV', 'development'); to your wp-config.php, while developing, so your Roots won’t look for the minified version.
- 
grunt devbasically will do all the work but* minifying; - 
grunt watchwill rungrunt devwhen something is modified; - 
grunt buildwill do all the work + minify, so you can send your project to your production server. 
The process as I understand:
- Add 
define('WP_ENV', 'development');to wp-config.php; - Work on your project with 
grunt watch; - Finishes the project -> runs 
grunt build; - Send the project to production server (where the WP_ENV won’t be “development”).
 
http://discourse.roots.io/t/how-to-correctly-add-bxslider-to-my-theme/1952/12?u=heitorss