You’re used to your iPhone saving GPS data along with each photograph it takes, and seeing its location when you import the picture in iPhoto. But photos taken with your main camera show up without a location, requiring you to manually set one for each picture.
In iPhoto you can just copy the location information from your iPhone pictures, but for that you have to remember to take your iPhone out and take a picture. Or you can let iTrackPhoto automatically generate images along your route, while your iPhone stays in your pocket. When you import these images in iPhoto, they’ll show up right next to your photos, and you can copy the location information from them, quickly and easily.
When running iTrackPhoto it uses the GPS hardware built in to your device. Continued use of GPS running in the background can dramatically decrease battery life.