The depth-sensing front camera on the iPhone X isn't just useful for unlocking your phone or making silly emoji clips. Eyewear maker Warby Parker has updated its Glasses app for iOS to include an iPhone X-only recommendation feature. Let the app scan your face and it'll recommend the frames that are most likely to fit your measurements. This isn't the same as modeling the frames on your face (wouldn't the iPhone X be ideal for that?), but it could save you a lot of hemming and hawing as you wonder which styles are a good match.
This is something of a niche use -- how often do you go shopping for frames, really? With that said, it illustrates how a depth-aware front cam can serve a genuinely practical purpose. If it can map your face and other objects in a scene, it can measure all kinds of data that just wouldn't be an option with 2D photos. You might not want to buy an iPhone X just for this, but you may get more value out of it as developers get a feel for what TrueDepth can do.