When a practitioner believes that a submission hold is locked in, he should apply reasonable force to submit his training partner. However regarding joint-locks, especially TWISTING ones(heel hooks, kimuras, toe holds, americanas etc) should never be applied 100% in a training environment.
An armlock for instance should not have excessive force applied to it if the arm is fully extended. Another example is a Kimura lock. Once a training partners hand has been put behind his or her back, actual force should decrease substantially even if the training partner is not tapping. Please keep in mind that in some circumstances a student might be unable or unaware of “when to tap”.
By adopting this philosophy to your submission holds before they are finalized you can study your opponent’s reactions and escape motions, and then work on countering their defense to your initial attack. This intelligent approach to training is safe, reliable and minimizes the risk of injury to one another. Remember that we are a team and are here to make each other better. If one person gets injured, the team gets injured.