The overwhelming majority of the time, I haven't needed DDU or anything similar. My usual driver update procedure is pretty straightforward:
1. Catalyst "Express Uninstall"
2. Reboot
3. Install new Catalyst
If you've got a bunch of custom stuff configured that you want to reset back to defaults, then running DDU might be worthwhile. Or if you're switching to a different AMD card and you want to reset stuff like Crossfire profiles back to their defaults. But for the most part, the built-in uninstaller works just fine as long as you're not careless with what you're doing to your system. I know some people will just install newer drivers on top of older ones, I've never done that. I always uninstall the old ones first. Custom app profiles & such are retained even with the "Express Uninstall" option, to the best of my knowledge(I haven't used the feature in a while, I use RadeonPro).
The only time I would absolutely recommend using DDU is if you're switching from AMD to Nvidia or vice versa. Then I'd say it's a good idea to get a completely fresh start, driver-wise.