Here's why. You cannot manage what you cannot measure. A while back I used to bike to work 22 miles and lost 20 lbs. However I stopped after almost getting hit several times and the breaking point was after my gf's brother's friend's dad was killed while biking (and the dozen or so bikers reported killed over that past year). At that point I decided it wasn't worth my life to work out via commuting to work on bike. Now I want to work out via biking on a trail, running on a trail and rollerblading, again, on a safe trail. But I need to quantify exactly how intense my commute was and see how much harder I need to work-out without that 22 mile commute. I need data!!! And yes, I'll have to make 1 last attempt on the bike commute of death to get the first batch of baseline data, but hopefully the odds are in favor that I'll be able to make that last trek without getting killed. If I don't reply next month, you'll know why. ;-)