From Clarius VisualStudio Targets project:
The out of the box experience for authoring templates in Visual Studio is a multi-step process that isn't very amenable to incremental improvements. An exported .zip file does not encourage rapid iteration ;).
An alternative way introduced in VS2010 was a new project template.aspx) to generate a project (or item) template output (its compressed zip). Yup, if that sounds weird, it's because it is. It's a project where you don't compile anything, but rather just work with the files with parameter substitutions.aspx) and the like, and where building means just zipping it. If you have just one template to distribute with your VSIX, that may be ok.