During compilation, all classes from all referenced libraries, that their full name (package + class) starts with one of the above prefixes, will not be included in the APK.
Why is it useful?
Smaller APK, faster compilation and faster installation. This is especially useful when referencing the large google play services library.
Removing libraries based on the selected build configuration. Like all other attributes you can use compilation symbols to add or remove this attribute.
Removing unsupported classes. For example, Amazon rejects APKs that include the RingtoneManager classes. So instead of modifying the Phone library, you can exclude the problematic classes.
As google play services is the main candidate for this feature, any prefix that starts with a dot will be converted to google play services package (com.google.android.gms).
If you are only interested in the maps functionality of google play services:
There is no relation between the classes and the permissions added.
Adding the Phone library will not add any permission to your app. Only when you declare a PhoneWakeState variable then the relevant permission will be added.