yeoman/generator-angular — pull request #142 by bfx81 (2013-04-06 23:01:01+00:00)
Title: Prefer usemin to configure cssmin workflow

In development ('grant server') the user needs actually to reference the css, otherwise other files in app/styles (bootstrap.css just to name one) other than main.css will not be used.
An @import url(bootstrap.css) in main.css is not the best thing because this will be included in the concatenated output file.

So IMO a "usemin" configuration like this is more appropriate.