The loud/soft dichotomy as a means of heightening tension -- that's a common device used in orchestral music since... well, pretty much as long as we've had orchestras. Rock and folk have pretty much abandoned this, which is a shame. Radio stations compress the hell out of everything to the point that you wouldn't hear this even if it were used.

Of course, much of it is left over from the vinyl era, when a quiet passage meant that the music was being overshadowed by clicks and pops. But CDs and their brood have overcome this, and modern classical albums take full advantage of it. It's a shame popular music hasn't caught up.

Many films -- particularly action and scifi films -- are afraid to have passages that are too quiet as well, which robs the work of scope and dimension.

It's a public speaking maxim that a good way to get a crowd's attention is to speak lower. They'll strain to hear you a little, and pay more attention to eke meaning out of your not-quite mumbling.
 

Creating dramatic tension for all the senses involved in watching a movie always makes for a better movie. Tension and contrast in light, color, sound, music, volume, pacing, story, character, etc., has to be considered every single moment of screen time without it becoming an obvious burden on the audience.