Yes and no! You can simply clean out the primer pockets and flash holes and go on and reload. However, tumbling the brass (or U/S cleaning) gives you a better look at the brass condition and can help identify issues which could spell trouble. Tumblers for walnut/corn media such as Lymann's turbo tumbler are cheap and it's hardly any effort, so I always tumble mine before de-capping (otherwise you end up picking bits of media out of primer pockets), then anneal every few firings. Many target shooters bin brass after one or two firings. Most hunters and local club shooters I know do not and clean their brass for the reasons already mentioned and because "they look nicer". It also helps limit the toxic contamination you pick up on your fingers when handling dirty cases, but it's good practice to wear nitrile gloves (and a face mask) when emptying a tumbler. The lead oxides from spent primers is highly cumulatively toxic. You do NOT want that stuff in your lungs.