Don’t obsess too much over the data unless you’re doing a structured workout and need to target a specific area. I only use cadence as a general indication of whether I’m mashing (RPM less than 80), spinning, or running at high RPM. I target 90 for the most part, but not to the point of paying much attention to it.
Of all the metrics I track, heart rate and power are the most important. If I’m doing a really long ride, I know how much time I can spend in each zone. If I’m training and targeting tempo, threshold, VO2 max, etc, heart rate and power are invaluable. I also use my computer to track my gears, which is a nice feature.
I don’t track speed at all, except that I generally hope my speed increases over time.
What you track and how closely you watch it depends entirely on what your goals are as a cyclist.