Great discussion.
I've been off the bike for years, and when I did ride regularly it was on my roadie...for a long time I used a computer for cadence and developed a pretty keen feel for my "normal" which is around 90.

I've since returned to the bike (a city-fied MTB) and have noticed (age has some effect) that I "spin" slower than I used to, but I do use the gears to find my comfort zone -- probably around 80-85.

As I've gotten some mileaged on the bike I have settled on the large chainring and middle cassettes for about 99% of my riding (it's real flat here on the Florida coast)...I've noticed too that I don't head for the "lower" gears as often.

Cadence is a beautiful thing. As you progress, you'll learn where your comfortable spin-zone (apologies to Bill O'Reilly) is and pick your gear for that. I will say that spinning at 90 or so rpm while on the grannie gears does look pretty silly, but it saves the knees!!