I know there are a lot of threads about this, but there seems to be no clear consensus (at least to me) as to what the advantages/disadvantages of upgrading vs doing a clean install as a new version comes out. I've heard two sides. One says that a clean install has only two advantages, preventing dependency problems (which may or may not occur at all), and to prevent the build up of cruft. The other side says that a clean install is necessary to take full advantages of new features, such as a change to the filesystem or changes to every package, such as adding PIE which may happen in the near future. This is what I'm specifically curious about.
Ubuntu currently uses PIE for only a few, security-focused executables (like sshd), but most aren't using PIE because of the large performance penalty on 32-bit systems. However, 64-bit computers don't have the same performance penalty. According to this, using PIE with everything "will eventually be made the default, but more testing is required". This seems like a pretty big change. So would simply upgrading be able to accomplish this, or by "made the default" does it mean only a clean install will have this? When the version of Ubuntu comes out with 100% PIE support, will I have to do a clean install or will the upgrade alone replace every file in /usr/bin, /bin, etc with the PIE version?