The only reason not to do the full range of motion is if you're cheating in order to get more reps or use more weight than you could with proper form. Repetitively shorting weightlifting movements can cause joint problems.

Move your body through the whole movement. There's no good reason not to.

The only reason not to do the full range of motion is if you're cheating in order to get more reps or use more weight than you could with proper form. Repetitively shorting weightlifting movements can cause joint problems.

Move your body through the whole movement. There's no good reason not to.

Further, what happens if you don't extend your joints fully? Use it or lose it--your body will stop being capable of going to full extension. Then you'll have to start shorting the movement more and more over time, until you are decrepit and immobile.