Why would you care in the first place? Because lower trapezius is essential for the correct functioning of shoulders.
Without proper anchoring of part of middle of shoulder blade with lower trap, serratus anterior can’t do it’s job properly, and the shoulder blade can’t rotate up to clear your arm to move up without unnecessary extra impingement, when doing overhead movements like loading a bag into overhead compartment on a plane, throwing the ball from the sideline any shoulder press movements at the gym, and exercises like lat machine pulls and pull ups.
How do you know lower trap isn’t working properly? If I ask you to pull your scaps together and down a little, and try and feel it between your scaps, and you can’t do it much, that’s a good indicator you are not using LT very well. Another way is doing, or trying to get into the position of wall angels. If you’re struggling to even keep the arms on the wall, that is another indicator of under used LTs. If that’s the case, and you had issues with shoulders, then that’s pretty good, as training the LT progressively to be able to those things can fix the issue.