System logging is for a variety of things: troubleshooting, checking boot up, seeing what processes are doing what..
It's logging, whatever you use logging for, that's what system loggers do
A lot of programs need a place to log things, but I'm sure if you are well versed you could send them to /dev/null instead of a system log. Alternatively, you could symlink your system log to /dev/null.
Anyway, should you turn it off? No. You don't gain that much (any?) of a performance gain from that.
Cool
