One of the big advantages of the iPhone and iPad is Location Services. Built into iOS 4 & 5, Location Services allow your iDevice to know where you are at any particular time. It uses both GPS as well as cellular tower and crowd-sourced WiFi access points to determine your location. This is particularly helpful for things such as weather apps, social networking apps and so forth so you can get local information no matter where you are and to get it without requiring your intervention. There are times however where you may want to disable this functionality for privacy or security concerns. Fortunately Apple has provided a quick and easy way to do this in the settings on your device.
To start, Location Services are found in the Settings of your iPhone or iPad under, you guessed it, Location Services. If you tap the Location Services menu you will see the master on/off slider for the service as well as the list of apps that take advantage of it that are on your device. Each app has a slider that allows you to turn on or off the service for that particular app. While disabling the master Location Service will disable all of the apps from accessing your location information, I have found that disabling it per-app is a bit more useful. For example, when I travel I often will disable to Weather location services so when I can see the weather back at home when I access the Notification Center without having to go into the Weather app itself.
By some of your apps you will also notice a compass needle icon by the on/off slider for the app. These needles give you a visual indicator of the type of location information is being used as well as when it has last accessed Location Services. For example, if you see a purple icon then that app is currently using the service to determine your location. If you see a grey icon then that app has accessed the service in the last 24 hours. If you scroll down to the very bottom of the Location Services screen below the apps you will see all of the definitions for each icon.
Location Services is a power feature of iOS and 99% of the time is a huge help rather than a problem. There are times however where being able to turn it off can be handy or give you an added sense of security as you travel about.