Hello,
Some folks almost make "Big Data Analysis" or "Deep learning" with sets / reps / measurements of all kinds (weights...). However, the simplest things are the ones which works the best. Body consciousness works great.
If one cycle ones training, then you do not need to note anything as there is an established frame to follow. E.g. Strength cycle then Power Cycle then a meet.
If you are on a long run routine, maybe it is more interesting to note once a week or something. Your performance - in terms of reps / weight - is not supposed to vary a lot from a day to another. However an each training session note on the forum can be useful to get some help or share feeling and information.
Kind regards,
Pet'