It surprises me sometimes how people think that Non return valves and control valves are as good as isolation valves. They aren't and whilst flow through a pump or compressor isn't common, can easily occur, even for small injection pumps if the system is shut in and then cools down - happened to me once and overdosed a section of fluid by >1000 times.... Actuated isolation valves are your only truly reliable solution.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way