Logging helps you to maintain logs in your app with in a file with the help of Logger framework. You can set the level of log you want in logger file, means debug level logs or error logs or info or warning etc.
This framework written in Swift allow you to set the properties for your logs like in which location you want to keep your logger file, what will be its name, what size of file should be, if you want to rotate files then how many files you want in directory to rotate.
You can log the file components.
Also you can trace the crash and exceptions if any and logger will keep maintaining a flag for you which tells about app did crash last time.