Why it's important. Why it's important.
Cadence is largely fashion.
As a less atheletically talented person, I disagree. If I only could have one function on my bike computer, I'd probably go for cadence. Monitoring my cadence is the best way I found to build up my cycling ability. As a beginning cyclist, I picked a nominal cadence that I was comfortable with, while riding on a level road, while in the middle of my available gearing. I had read somewhere that I should pick the cadence by imagining that I had a raw egg that I didn't want to break, between my shoes and the pedals.