Which brings up a question. When in a tank I normally sit in the top observer position and aim/shoot from there. I take it there's an advantage to be looking through the turret sight. Yes?
Ranging marks (in case of German tanks an adjustable gunsight with a great range finder functionality) and depending on tank a much better magnification
Panther, commander view of a medium distance tank

Panther, main gunsight view of the same target:

And is there an advantage when tanking to have view mode set to F4 ground vis? Silly questions perhaps but I'm rarely in a tank fighting other GV's
You can see the ground details farther out. When engaging ground targets, use ground vis.