To me the more interesting scenarios aren't related to size.

* Being able to embed comments which aren't visible to the world is very useful.

* Being able to remove non-important whitespace removes clues on the complexity of generation (though it's a super-complex thing to actually remove only the non-important whitespace thanks to <pre> and CSS styling).

* Linting is another area where things are interesting too. Validators might tell you if your HTML is well structured per the specs, but my js skills and habits have improved as a result of linting. The process might tell you that it's best practice to use readonly instead of readonly="readonly" on an element or similar. Sure, not directly related to minification, but the parsing needs to be done already.

* Minification adds some security through obscurity by making stuff like XSS attacks slightly more difficult (if you use name/id/class mangling). I've only seen this in practice on gmail (most gmail browser addons/scripts break every couple of months when google changes something that alters the generated button ids)

I haven't seen minification done on raw HTML, but have seen non-html solutions used in order to be able to include comments - this is a bit dumb to me.

I've used HTML preprocessors to concatenate separate (single page app) html resources (templates) for delivery, so the pipeline's already there.