I added myself to both the dialout and tty groups on a stretch installation in order to use the serial ports from the user level. It works fine. Then I looked at a debian jessie installation and found that I had only added myself to dialout and it still works fine.
What is group tty actually for? This is more of an idle curiosity question than it is one of something's broken and I need help. I am a retired systems engineer who setup unix systems for coworkers to use so I know you can sometimes have too much power at the user level and accidentally make it easier to make a mess of things. Thank you. Martin McCormick