Many grad students and post-docs are seeing faculty candidates come in and give jobbe talks in their departments, and it is really instructive to see both good and bad ones.
But don’t underestimate how much preparation and practice it takes to give a good job talk. While it certainly helps to see the mistakes others make and to tell yourself not to make those same mistakes, it still requires substantial time and effort and lots of feedback from others after giving multiple practice talks to ensure that you don’t.
Think about it this way: It’s really easy for any golfer to see the difference between Tiger Woods’ swing and the swing of some duffing geezer down at the driving range. That doesn’t mean any golfer can just get up on the tee and swing like Tiger at will.