I have 2 computers on the bike, one that also has a heart rate monitor. During a ride I rarely watch its display, I have the HRM set to sound an audible alarm for when I cross into the VO2max zone. I like to alternate shorter rides where I push into VO2Max and longer rides where I want to stay below VO2Max.
I use the other features after the ride to see how I've done, max speed, average speed, average HR, max HR, trip distance etc. I find the trends useful to monitor my fitness level (lack of more likely).
The other computer is set up as a cadence meter, that one I glance at frequently. I use it to determine when to shift gear.