From an instructors teaching point of view, its important that students actually practice operating fuel cocks, especially at schools where the cock is not routinely turned off after flight, otherwise you can be asking a student to turn tbe fuel off in an emegergency situation without ever having shown him how to actually do it and on some a/c turning the fuel cock off can be difficult while flying the aircraft. especially if you have never done it before!
I very much agree with this sentiment. Students should be taught and practice not so routine pilot actions during their training. I think this extends beyond just fuel cocks to pilot actions like: Shutting down and
securing the engine in a glide, feathering and unfeathering a propeller on a twin, gliding a C/S prop aircraft in full coarse pitch, actually using landing gear manual extension controls, running a tank to dry in flight and changing to the remaining fuel, flying with the alternator selected off, effectively discharging a fire extinguisher, properly completing a journey log entry, and perhaps even actually applying something from the first aid kit. None of those should be done by the pilot for their first time, when urgency demands it. But none need be done routinely either! And, in Big Piston's theme, I would hope that the type competent instructor could demonstrate each of these, and explain the factors associated.
Cessnas are known for not feeding fuel evenly - we learn to live with it. If it is frustrating the pilot, they certainly can use the fuel selector to modulate fuel flow as desired. The left wing vent can be out of position, which can affect fuel flow, and flying with a bit of crap can also. This is perhaps more noticeable to Cherokee pilots who are more accustomed to the fuel going exactly the route they select!