An obvious use could be as a library building tool. i.e. All the macros could be restricted to the internal methods used to construct the library DSL. All the public methods could look like standard js, and the library users would be none the wiser to the magic used internally to make the library construction more efficient.
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I like sweetjs which brings syntax macros to JavaScript. It hasn't got much traction yet, but I'm convinced someone will do something neat with it.
http://sweetjs.org/
An obvious use could be as a library building tool. i.e. All the macros could be restricted to the internal methods used to construct the library DSL. All the public methods could look like standard js, and the library users would be none the wiser to the magic used internally to make the library construction more efficient.