Your brain will remember the LAST thing you did on a movement pattern. If you hit a sloppy lift or miss one, even if it's supposed to be your last set you should reduce the weight and get one or two perfect sets, even if it's a light weight. If you finish on that bad rep, that's what the nervous system will remember and you will gradually degrade your form.
The last thing you do on a movement pattern is what will have the greatest impact on motor learning.
- Christian Thibaudeau
For example - squat, deadlift, bench press and chin-ups
You need to learn the perfect techniques to perform all exercises perfectly. If you did a sloppy set and reps, your brain would remember what did you do at the end (the last rep).
Therefore, we need to perform perfect reps at the end of the set, and even the weight is lighter.
Don't pretend you did the session.
When you've finished the last set, if you don't think the form is perfect, you still want to improve it before you end the training session, you can do one set with the lighter weight with perfect form as a finisher.
For example, I made a personal best (PB) 225lb on my snatch.
I know that was not my perfect form.
Maybe it was an accident.
If you ask me to repeat to lift the same weight again,
I probably could not make it.
Therefore, I would lift 185lb or even lighter weight at the end of my training session to ensure I've got the right technique, but not by accident.