I don't see why not. What's wrong with it?

Very subjective, but I feel like if you're going to write HTML, you should just write HTML. (or possibly something like markup or restructured text)

I just feel like writing code to generate document markup doesn't really fit the model of what it is. I can understand why coffeescript -> javascript fits the same mental models though.

I agree with you if you need a template for a blog or sales pages or some other light markup. But if you have very complex HTML that renders controls, graphs, crud - dense complex things which are less HTML and more of rendering commands in form of stacked divs. Then this wins out.

For me, its kind of redundant. Also, I've been mind melded into an MVC mindset and can't see how this would be helpful to me.

Is there any speed gains in terms of page weight or loading times?

I dont have any numbers to back this up but: * templates get compiled to js * there is no magic the code you write is the code that runs

It feels faster because there is no interface between you and the template language - because there is no language its just coffee script.