The viewpoint on such things will likely differ from one modality to the next. From the perspective of yoga and its applied anatomy I’ll offer the following. Please bear in mind I’m intentionally over simplifying.
Muscles are designed to a) protect the bones they surround and b) move those bones through a plane or space. Muscles are the primary system used to move the musculoskeltal system AND they (muscles) connect to bones via connective tissue - in this case tendons.
When the primary system fails there is a weaker, less able secondary system. When the less able secondary system is called upon in an “emergency” it is designed to assist briefly in order to prevent calamity. When the secondary system is used over and over (instead of the primary system) the result is irritation/swelling/damage to the tendon. When this happens the only doing that facilitates healing is the doing of not doing.
In an asana practice which balances effect and safety appropriately there is no stretching of tendons or ligaments. The awareness of the student is placed in the muscle and the action is kept from the connective tissue. This is a relative concept in much the same way isolating a muscle is a relative concept. Some action will absolutely go into the secondary system. But it is not at all the intention and should be avoided.
There are, of course, some asana practices where effect is far greater than safety (imbalanced) and others where safety is far greater than effect (also imbalanced). In the former, hammering the secondary system is unavoidable.
Loose tendons and ligaments destabilize the musculoskeltal system. Ligaments and tendons foster joint integrity. Such tissue, when healthy, should not have laxity.
