A template allows all the icons to have a graphical consistency. Before producing the template the style or overall look of the icons had to be decided upon. At SAS Institute the decision was to use an illustrated 3-D look. Once the style was chosen a template was created. To be most compliant there should not be any bleeds.
Consistency is the goal.
Once you've decided on a way to represent an object or action, use it throughout your icon designs. You want your icons to reflect your style, but you also want to follow established usage. Choose the right image to depict the right action. Choosing a Palette. This depends on your primary platform.