How Are End Effectors Handled With Retargeting?
Do tall characters run faster, can they still hold the same props - these are questions that may arise when working with retargeting. In short, there is no automatic work happening and it is up to the user to decide what they want it to do.
One method that can be taken regarding the holding of props is to create a separate chain of bones that follow the hands in the original animation, called "Hand IK Bones". Then retarget the body and arms, but not the "Hand IK Bones", so they remain identical after retargeting. This will allow you to have characters of different proportions manipulating the same props (for example, reloading a rifle).
Having a separate chain of bones allows you to switch smoothly between FK and IK easily when you want to (for example, you would want the Hand IK ON when reloading the weapon, and OFF when reaching for a magazine in a pocket).
The system is very flexible and can be customized to fit your needs. Perhaps you only want the left hand to be IK and the right hand to use its FK position, but IK rotation. Feet are sometimes handled this way, sometimes not. When stepping on a very precise prop, you would want to turn on IK; when you are just running around, you would want to use the FK, so you do not end up with a bow-legged character (or the opposite).