Just depends on what your after from riding. I can see and appreciate the notion of just riding with the wind!!
However, I'm a numbers freak and even just purchased an altimeter. I like to know the per cent grades of the climbs I'm doing, amount of climbing I've done for the day, etc. However, I don't watch anything but cadence, per cent grade and sometimes distance during a ride but I use all the other information to help assess my fitness. It's been very rewarding seeing the numbers continue to improve over my 4 years of riding. By keeping the numbers, it's easy to see progress or backsliding monitoring similar routes and rides from each year.
I've taken the data and charted graphs of miles per month for each year and so far I've always ridden more miles in a month than that month for the previous year. You can also determine what your overall mph is for the year by looking at total miles versus time, etc.
Again, just depends on what you're after!
By the way, the steepest climb I've measured this year has been 21%...It wasn't too long but long enough to really hurt!!!