A log is useful because it preserves context: what was planned, what was completed and why the load changed. The next session can then continue an observed process instead of starting with another guess at the working weight.
Memory keeps a few strong sets but loses ordinary work: later-set repetitions, technique changes, unfinished assignments and reasons for reducing weight. After several weeks, the previous session becomes a vague impression and the load is selected almost from scratch again.
A completed weight alone does not show whether the session was successful. A sensible reduction can be a better decision than forcing an old assignment. Comparing the task with the result reveals where progress occurred, where adjustment was needed and what should be repeated next week.
Strength and work capacity do not change in a straight line. Compare several weeks of working weight, repetitions, volume, reps in reserve and estimated one-rep max. This separates a persistent trend from one unusually strong or weak day and reduces the need to test a maximum.
The record should be short enough to maintain and complete enough to support the next decision.
In GYM Planner, the log is connected to weekly planning, so one entry helps prepare the next decision.
