Ticket barriers were recently installed by CT at Lincoln. They do still have a member of staff on duty to assist people with season tickets, large size tickets, or whatever.
Chatting to the staff member one day, she told me that ticket revenue had increased by 50%! Lots of journeys were being made between the many local stations on busy trains where the passengers knew the conductor could not get to them before their stop.
I am definitely in favour of barriers as I do not like people travelling free whilst I am paying.