10mm vs 8mm motor shafts performance difference

I was wondering if there was any difference when it comes to having a motor that has a bigger shaft?

Bigger shaft means more torque. but heavier motor

Maybe you need to expand on your reply a little more to avoid confusion.

A larger diameter shaft doesn’t give you a gift of more torque output. Torque is a turning force created by electromagnetism inside the motor.

Larger shaft diameter certainly is stronger and will perform better under increasing torsional loads.

If your system and motor is designed to be a very powerful with high torque output you may certainly want a stronger shaft to handle the torsional loads and deliver the torque with less chance of failure.