It's good airmanship to test both tanks feed ok before flight.
If you switch tanks on the ground before take off you must do a power check afterwards! If anyone doubts this try turning the fuel off at 1,200 rpm on the ground and time how long the engine will running before quitting then do the same but immediately after you've turned the fuel off do a power check. In the latter case the engine will quit within a fews seconds of turning the fuel off compared to at least a minute or so when the engine is at 1,200 rpm.
Some checklists that are around are full of holes because they are someone's opinion on how the aircraft should be operated - if in doubt consult the Flight Manual/POH.
The problem with fuel tank selection arises (usually) when the a/c is on level ground when you decide to select the "least tank" prior to start. You then taxi out and park the a/c on level ground for the runup and then many checklists say select "fullest tank" - you then look at the fuel guages and you are already (apparently) on the fullest tank! It would be better if the checklist just said "select opposite tank". Then it would be better in the pre take off check if the checklist said "Fuel - NOT off" etc