From roughly May through August, low coastal stratus pushes into the LA basin overnight and sits there until mid-morning. Locals call it May Gray and June Gloom. The layer is usually only a thousand feet or so thick and there is brilliant sunshine on top of it, which is precisely what makes it so frustrating: the weather is beautiful, and you cannot legally get to it.
A VFR pilot looks at an overcast at 1,200 feet and cancels, or waits until eleven. An instrument-rated pilot files, departs Van Nuys on a clearance, climbs through about ninety seconds of gray, and is in clear air above it. Same airplane, same morning, completely different day.
That is the practical case for the instrument rating in Southern California, and it is a better one than the case usually made. Nobody in Los Angeles needs an instrument rating to fly in thunderstorms. They need it so that a predictable, thin, entirely benign layer of cloud stops dictating their calendar four months a year.
The second argument is precision. Instrument training rebuilds how you fly — altitudes held to fifty feet, headings to five degrees, approaches flown to published tolerances. Most pilots describe it as the point at which they stopped feeling like a student.