Well, sound pressure levels are a matter of public health. Prevents knuckleheads from damaging your hearing just because they think it's a good idea to blast sound way beyond sensible levels. And yeah, they enforce these laws. As a house engineer, it also gives me the tools to have some control over stupid engineers that rely on sheer SPL instead of being able to actually mix stuff. Plus the newer regulations setting the max levels in dBC instead of dBA have the added benefit of controlling the over-reliance on subwoofers. Hence better mixes. Win win.