They mess with the natural landscape and can lead people off course. It's better to use maps and leave no trace.
I was trying to follow the marked trail in Red Rock Canyon last week. My phone died and I had to rely on my old topographic map. I misread a contour line and ended up off route. After an hour of bushwhacking, I came out on a cliff edge with a stunning vista. It wasn't on any guidebook or app I've seen. Now I think getting lost a little can be a good thing. I'm adding extra batteries to my pack from now on.