Necessary? No. Desirable? Yes.
My regimen for range brass:
Ultrasonic cleaning to get the crud off
Resize/deprime
Tumble with walnut hulls and jeweler's rouge
Ultrasonic cleaning to get the abrasive dust off
Ready to load!
I use Simple Green or 409 as the degreasers in the ultrasonic wash, but any surfactant will do.
Will the shiny brass load and shoot any better than the cruddy tarnished kind? Probably not, but you will see any defects right away - the split necks, the shiny rings of impending case-head separation, etc.
Worth it for me.
LT