A workout log preserves details that memory may miss: exercises, sets, repetitions, weights and setup notes.
Compare the same task
Use the same movement name, unit and equipment convention across sessions. If a variation changes, identify it in the exercise name or a note.
Record what happened
Suppose three sets finish at 8, 8 and 6 repetitions. Keep those results rather than replacing them with three planned sets of eight. This is an example of recording, not a recommended workout.
Ask a specific question
Use the record to check what changed in a particular exercise. A higher total may reflect more entries or different equipment; it is not direct proof of muscle growth.
Make it repeatable
Review the previous record as context, then enter today’s results. Weights supports routines, set logging and notes, but a log does not select a suitable training program for you.