In the setup for the deadlift, we sometimes see the problem of people setting up too close to the bar, and taking a look at your shin angle can help identify this problem. This problem is usually born of good intentions and is similar to the “shoving the knees too far out in the squat” problem (yes, that actually does happen with some people). We know we’re supposed to shove our knees out, and then we accidentally - and almost always unknowingly - overdo it. Likewise, in the deadlift, you know you’re supposed to set up close to the bar, and then you accidentally overdo it by setting up too close.
Remember, step #1 of the deadlift setup is “Set up with the bar over your midfoot - with your shins one inch from the bar.” It is NOT simply “Set up close to the bar.”
This is where looking at your shin angle can help. In the deadlift setup, at the start of the pull, everyone will have a small shin angle (measured from vertical) if the bar is over midfoot, i.e., the shin will be angled slightly forward, but the actual amount will vary slightly with anthropometry. With this variance in mind, there is no single shin angle that will be correct for everyone, but there is one angle that is wrong for everyone, and that’s zero degrees. In other words, if your shins are completely vertical as you’re about to pull the bar off the floor, the bar is in the wrong spot with respect to the middle of your foot.