rtkit-daemon is very chatty (read: spammy) by default.
Jul 07 21:29:08 solbox rtkit-daemon[1134]: Supervising 12 threads of 8 processes of 1 users. Jul 07 21:29:08 solbox rtkit-daemon[1134]: Supervising 12 threads of 8 processes of 1 users. Jul 07 21:28:42 solbox rtkit-daemon[1134]: Supervising 12 threads of 8 processes of 1 users. Jul 07 21:28:42 solbox rtkit-daemon[1134]: Supervising 12 threads of 8 processes of 1 users. Jul 07 21:28:38 solbox rtkit-daemon[1134]: Supervising 12 threads of 8 processes of 1 users. Jul 07 21:28:38 solbox rtkit-daemon[1134]: Supervising 12 threads of 8 processes of 1 users. Jul 07 21:28:13 solbox rtkit-daemon[1134]: Supervising 12 threads of 8 processes of 1 users. Jul 07 21:28:13 solbox rtkit-daemon[1134]: Supervising 12 threads of 8 processes of 1 users. Jul 07 21:28:08 solbox rtkit-daemon[1134]: Supervising 12 threads of 8 processes of 1 users. Jul 07 21:28:08 solbox rtkit-daemon[1134]: Supervising 12 threads of 8 processes of 1 users.
The tweak quietens it down considerably and makes the systemd journal more readable.