Ring-a-ding-ding, I've also been repairing computer for over 20 years, and I disagree with your position. It's not about shaving seconds; it's about system maintenance. That's how you keep your system from crashing: downloading security updates, cleaning house, and a periodic drive defraging. (Let me guess, that's pointless too.)
You do not need the the registry keys of every piece of lousy software, you ever installed and uninstalled, bloating your registry. Some of these programs leave well over 20 registry keys that do nothing but bloat the registry; that's beside all the folders and files left behind by many of them.
The system registry is a bonzai not a junkyard. Just like Thunderbird 1 and 2.0--after about a 1000 or so emails you start having parsing issues and the next thing you know your inbox is corrupted.
Download revouninstaller, and then USE it to uninstall some of your programs and see how much crap is left behind: registry entries, folders and files. Actually, use it to uninstall an instant messenger. (LOL)
It's 2010, times have changed and the software has vastly improved since the days of Yor. A monkey can maintain the registry with the right tools--without needing to know a whole lot; eusing and revouninstaller create backups too.
This is just basic system maintenance in my opinion. You tune-up your car to prevent problems. You don't drive the hell out of and then pay a staggering repair bill; you pay a little for the tune-up so you don't have to pay a lot for the transmission or a new engine.
I haven't destroyed a registry since Windows 3.0, by the way.