Heh I feel you, when a new Ubuntu comes out sometimes I just fresh install just cause you never know, though I have upgraded in the past. If you install Ubuntu and then want a new Desktop Environment, it doesn't feel quite right, because the original install defined defaults that the new DE isn't setting itself for / against.

On Windows I don't reformat anymore like I used to, and I used to reformat a lot because I would disable "useless" Windows services to save on RAM (back when I had 3GB of RAM, and then 8GB). When I stopped doing that, my OS was working fine for years and years.