Here is what United's website states for "TSA PreCheck Touchless ID":

"If you have TSA PreCheck and are departing from Chicago ORD, you can use your face to check your bag. With TSA PreCheck Touchless ID, you don't need to show your boarding pass and physical ID at bag drop shortcut. We plan to add TSA PreCheck Touchless ID to more bag drop counters, security checkpoints and boarding gates in the future." It states so long as you have your Known Traveler Number and Passport ID in the United app and agree to terms, you are eligible for this.

So basically it allows you to skip scanning/showing your boarding pass and ID. Not a huge time saver but could be in the future for getting through TSA - not having to hand over an ID or scan a boarding pass to get through the initial verification before the x-ray system. As noted in the chain, this could mean e-gates to get to the x-ray system in the future, which could on paper save time. I know some scoff at how much time will be saved, but personally not having to pull an ID out of my pocket wallet or pull up my boarding pass (leave my phone in my pocket) is a convenience I would appreciate.

I'm flying this evening out of ORD and need to check a bag. Will give it a go.