I'm a stickler for READING. Like reading instructions. My hope is that the guy that wrote the book knows more than I do.
Anyway, my first loading manual was from Lee. Also, it came with a "kit" and the Lee primer pocket cleaner was included.
So, I cleaned the pockets. My bench has the small and large tools embedded in the board between the sizing die and the primer setup. It takes me literally no time at all to do it. I don't think I ever loaded a box without doing it.
I corncob clean before resizing, so my primer pockets are not exposed. Also, no media is EVER stuck in the flash hole.
Is it necessary? Maybe not. Will I stop now after reading this thread? No.