NEVER leave your Tomcat Output window open, right? (in the Control Panel)
Everyone knows this by now, right?
Tomcat window scrolling slows down your system big time.
Eats CPU
Worse the more scrolling happens - ie. if your window is big, more scrolling, more cpu, more slow everything.
Open when you need it - always close when done with maint. or debugging.
I never run as a service, so cannot comment on additional impact logging to file does, if any.