This image explains it pretty well, you typically chose between Forward Kinematics, or Inverse Kinematics, depending on what you're trying to accomplish and how

This image explains it pretty well, you typically chose between Forward Kinematics, or Inverse Kinematics, depending on what you're trying to accomplish and how you want it to look like: https://www.researchgate.net/profile/Ebrahim-Poustinchi/publication/341173542/figure/fig1/AS:888016843329536@1588731122232/Difference-between-IK-and-FK-solutions-for-robotic-motion-IK-interactively-moves-all-the.jpg https://www.researchgate.net/profile/Ebrahim-Poustinchi/publ... (imagine the robot parts are human limbs, same thing applies :) )