Completely agree. If you're not measuring your performance now, you're obviously not serious about beating it next time.
Logs are one of the main differentiators between people who exercise; fartassing around doing whatever they feel like on a given day (chest and biceps anyone?) as opposed to people like us who train. We have specific and measurable goals which we work toward. I had a really hard time trying to exercise, it all seemed pointless. When I started to train, lifting became much more enjoyable.