This plugin changes the behavior of Sass's @import directive so that if the same
sass file is imported more than once, the second import will be a no-op. This
allows dependencies to behave how most people expect them to behave and provides
a considerable performance improvement for some sass projects.

Note: Although this plugin is maintained by compass, it can be used without
compass in any Sass-based project.

WWW: https://github.com/Compass/compass/tree/master/import-once