I uninstalled Brave and after it completed it left a folder and a set of files in “C:\Program Files (x86)”. I examined the registry after uninstalling and the Brave uninstaller doesn’t appear to have removed any of their registry entries. There are many, many registry entries for Brave after uninstall.
I had uninstalled and re-installed Brave in order to try and fix some problems with Dark mode not resetting when I change the appearance back to Light mode. It made no difference uninstalling it and after re-installing it Brave re-opened with the same pages I had up before I uninstalled it and the broken Dark mode was still active.
In short, uninstalling Brave didn’t remove much of the stuff it added and now it is only partially uninstalled. I can’t get back to a clean install as if I had never installed Brave so I will never be able to reset my Dark mode display settings back to Light mode.
By not removing your files from C:\Program Files (x86), you have use up valuable disk space. By not cleaning out the registry, you use up valuable disk space, you make the registry all that much larger and theoretically, at least, slowing registry access for all other programs on the machine, Some of this clutter left behind makes it impossible to re-install Brave cleanly from scratch. It’s also just really bad programming practice to not clean up after yourselves.