Main thing is being able to share the logging stuff between libraries so something like slf4j and then various actual implementations of that facade (which log4

Main thing is being able to share the logging stuff between libraries so something like slf4j and then various actual implementations of that facade (which log4j is one of) in jvm land. There is also lots of stuff you might want a logging library to do that while not very hard would be annoying to do yourself for every project like log file rotation, switching log level while the application is running, optimizations (like in c/c++/rust you might compile for INFO level and drop all the DEBUG and TRACE level logging from the binary), different log levels for different parts of the app (including dependencies), etc