This file configures a Grunt task called "sync".
This task synchronizes one directory with another (like rsync). In the default Sails asset pipeline, it plays a very similar role to tasks/config/copy.js, but copies only those files that have actually changed since the last time the task was run.
Specifically, its job is to synchronize files from the assets/ folder to .tmp/public, smashing anything that's already there.
For additional usage documentation, see grunt-sync.
An example of this file can be found in our sample app repo, here.