One of the problems Ubuntu users get at first after installation, is that they don’t see thumbnails in Nautilus – you can’t see your photos, videos or such like. This happens, because the .cache/thumbnails is still owned by root. The ownership is not transfered to USER while installing. This has to be done manually after installing Ubuntu. If the release team members come here, they should make a note to rectify this.
The solution for installed systems;
Nothing in the user’s home folder should be owned by root, even though the user’s home folder (username folder) is owned by root.