I use it for a few things, like people above said I use it for the cursor. I have all me apps in folders with other apps that are similar, like a games folder or a shopping folder the good thing about 3D touch is that if you 3D touch on the folder it shows you which apps have notifications which is great for the folders that have alot of apps in it because I don't have to spend alot of time scrolling to find my application.
Edit: also use it to adjust brightness of lights in house.