Android Wear is designed to keep you appraised of what's going on with your phone via notifications and cards, but that's not all it's good for. There are already a few apps that let you tweak settings on your phone, and now Wear Hotspot lets you toggle the hotspot functionality. It's actually a pretty good use of Wear.
You can launch the app by finding it in the list or asking your watch to open "Wear Hotspot." Just tap the button that pops up in the app, and the phone's hotspot should flip on. Tap it again, and it shuts off. This doesn't magically enable tethering if it's blocked on your account – it only toggles the local setting.
I can actually imagine a few cases someone might want to use this. If your phone is sitting across the room on the charger, but you need its internets on another device, you can just toggle the hotspot via the watch. You know, because who wants to get up? Yuck. The app was developed with a Verizon Galaxy Note 3, and I tested it successfully on a Nexus 5 with T-Mobile service. Your mileage may vary, though.