I am running on a Windows 7 machine and my tmp folder is getting rather large(400MB). What is the purpose of this folder and can it be purged.
tmp can (and is automatically) purged. It is used to process the trees and merge them together. If you were not on Windows, it would use symlinks by default and therefore much less actual disk space. To use symlinks on Windows, however, you must follow the directions here: http://www.ember-cli.com/user-guide/#symlinks-on-windows