A couple of ads, one on television and one on radio, show why compound-modifier hyphenation is more than just an esoteric issue confined to the nerds of the written word.
There's the Geico ad on TV in which the dorky executive and the gecko go door to door to charm customers, including reading to their children. One line from the fake storybook says something about a "small car insurance bill." The written equivalent would be "small-car insurance bill" -- an insurance bill for a small car. Obviously, the actor was supposed to say "small car insurance bill," as in "small car-insurance bill," as in a small bill for car insurance.
Another ad, on a local radio station, for a product I can't remember, mentions "high energy efficiency." The meaning, of course, is not high-energy efficiency, as in efficiency that's particularly energetic, but rather "high energy efficiency," as in energy efficiency that is high. (No hyphen needed, though "high energy-efficiency" would be an acceptable style decision.)
The fact that "small car" and "high energy" are oft-heard word pairs makes these pronunciation mistakes especially annoying, though perhaps they contributed to the errors. My point is that compound-modifier hyphens, or the lack thereof, affect the way phrases are pronounced as well as the way they're read by those of us who can do so without moving our lips.