Save for the rare exception, the camera on the smartphone in your pocket is almost surely without the gear required for optical zoom. It's just not part of the ironed-out blueprint for today's smartphones—high-end or otherwise. And that right there is your reason as to why the camera software on board allows for digital zoom
Now, digital zoom ain't nothing like optical zoom. In essence, you're cropping a high resolution image and sacrificing some detail in the process. But in some cases this may well be worth it—especially if you'll be cropping post-shot anyway. There are other reasons too, like setting proper exposure for the subject of interest and getting just the right perspective. And if none of these apply, then you might simply want to get closer to the subject.
Regardless of all this, there's still a stigma attached to digital zoom. And given how it can butcher quality, that's not surprising. But is that stopping you from using digital zoom? Let us know by kicking in a vote right below!