What did you learn from your HRM?

i don't use HRM per se...i have the Body Media thingy ...so right before i step up in the gym , i reset the "trip" button - so it tells me how many calories i burned during my workout of cardio and weights ....60 mins of "heavy" lifting & 30 mins of the treadmil or eliptical normally burns about 525 calories ....i ONLY wanted to know this info so that i could better determine if i could eat that cookie or not ....i've evolved into not ALWAYS eating ALL my calories back and it seems to be working !!