Cadence is just a tool/technique/skill, one of many things that you use to try to optimize your cycling. A faster cadence magnifies your pedaling flaws. If you bounce at 90 rpm then you're not pedaling very efficiently and you're not getting as much out of your fitness as you can. Cycling is a form-oriented sport. Bad form is very hard to correct because it's hard to focus on something so fast and repetitious as pedaling. The better your form the broader your potential. Poor form is an immediate limiter in potential. It doesn't mean you'll be bad, it just means you won't be as good.

To work on improving cadence you can spin well above your goal cadence. Just like intervals improve speed you can do "cadence intervals". Try to sustain a much higher cadence, smoothly and fluidly. When I started racing I tried to finish an hour with a 120 rpm average. This meant spending most of my time at 125+ rpm. After that 90 rpm felt slow.

You can also use a trick where you overgear first then shift down. Push a bit at a lower cadence (relatively speaking), so use a bigger gear at, say, 80 rpm. Then shift into a lower gear. It'll feel a bit easy. Don't look at your computer, just maintain perceived speed. You'll fine that your cadence is higher than you expect.

Ultimately cadence itself doesn't improve your cycling. It's just one part of your whole cycling repertoire. However a fluid and efficient pedal stroke will improve your cycling, allowing you to increase your speed and efficiency dramatically (I'll say that for an average rider in their 20s to 40s I've seen about an 8-10 mph increase in maximum speed after doing speed work, and we're talking normal riders). So will putting less load on your muscles during a ride - spinning faster puts the load on your aerobic system, allowing you to respond quickly to pace changes and such. You want your legs to be "cadence-elastic", able to pedal from 50 rpm to 130 rpm under load, up to 200+ rpm with little/no load.