Cacti stores all collected information via RRDTool into files called rra. The RRDTool requires some parameters in order to create these rra files. Whenever we want to add a new device or create a new graph, we have to input these parameters. Inputting these parameters manually is flexible, but not very user friendly, and there is always a chance of error. Using templates, we can easily overcome this problem.

Read the full thing at http://www.packtpub.com/creating-using-templates-with-cacti-0.8