I've kept one for the past 25 years and find it to be a useful and motivating tool. Recently I totaled the cumulative mileage and found that I had run just over 51,000 miles. After calculating the number of trans-American trips this would have amounted to, I wondered if there was some kind of extended warranty I might be able to purchase to cover replacement body parts. My non-running friends are quick to point out that anyone who runs 51,000 miles ought to take out a warranty covering the region of the body above the neck. Actually, keeping a log of your workouts is a good way to improve performance and reduce the frequency of injuries.
Most athletes try to follow a particular training plan in order to achieve personal goals.
The log serves as the record showing actual workouts. This data can be compared to what was planned to help keep the runner on track. A daily log can be as simple or as complex as you want to make it. Basic entries include date, miles run, and any special notes such as weather, hills, speed workout, etc. If your are into high tech, you may want to record heart rate.