Why do some people use third party logging libraries?

Well, some are faster than NSLog, but I like them for the ability to tweak the various levels of output to the appropriate audience as well as build log files for export when unexpected issues arise (crashes automatically upload them to my analytics). I'll collect all the noise from my testers and only errors from my general users, often with some sort of toggle to enable in-depth logging, that can be submitted through the app when other issues arise and they reach out to me.

Apple also has introduced a new logging framework within iOS, in iOS 10, called os_log and they suggest using that but I have yet to get the opportunity.. it very well could be garbage and the reason iOS vomits all over the debugger now.