Since smartphones became the cell phone form factor of choice in the late 2000s, applications have been a necessity in the daily lives of smartphone owners. We have all heard the phrase "there's an app for that." Google Maps is a prime example, since getting to a new destination today is mostly accomplished using directions from this ubiquitous app.
What may be less commonly known is that the technology used to provide the phone's location is not dependent on cell towers. Unless you have a satellite phone, your cell phone uses land-based cell towers to make phone calls, send texts and access your carrier's data network. However, just like a handheld GPS, your smartphone has GPS hardware that determines your location using satellites.
This has paved the way for smartphone applications specializing in "offline" navigation and mapping. Google Maps is great for providing directions, but what happens when your cell reception drops out? This is where applications with "offline" capabilities come into play. These applications allow users to download maps to their phones and make use of the internal GPS to navigate when cell reception is not available. Since GPS technology uses satellites, their service area is essentially the entire surface of the world.
That wide service area is essential for many uses. When you are hiking/backpacking in remote areas, it will help you determine where you are. Any serious hiker or backcountry traveler knows that once you hit the trail, a cell phone is virtually useless for accessing most applications, making phone calls or sending texts. Companies like Avenza have specialized in GPS-enabled maps (in PDF format) that can be opened on virtually all smartphones. This allows hikers to check their progress and verify they are on the right trail to reach their desired destination. Traditional GPS companies probably don't want us to know about this, since it begs the question of why one might actually need a traditional GPS receiver.
For scientific types, modern GIS have been making use of phone applications to streamline data collection for environmental or field based jobs. Individuals in these jobs often need to collect standardized data in remote locations or areas where cell phone service is less than reliable. Using applications like Survey123 for ArcGIS, technicians can download survey forms, fill them out on their smartphone, and associate the data with a GPS location. This is a common use in the utility and environmental industry where knowing where assets or features of interest are is a must.
For those who like documenting their life on Instagram or another social media site, the smartphone camera can make use of the internal GPS to tag a location to the photo. So if you are in a bad service area and taking photos to upload later, the social media application will still be able to tag your location.
These are only a few of the more popular uses; if you think of others, there is likely an app for them.