Probably not as vital as some think. But if you reuse brass often you want them as clean as possible so you can inspect it. If you use it a couple of times and then toss the casings it's not a big deal.
That being said...I'm cheap. I use a thumpers tumbler, steel pins, a bit of dawn and lemishine for my cleaning. Deprime first and the casings look new after 2-4 hours of tumbling....often better than new.
But I hate spending money for brass I already have.