I've asked to see any system logs or screen shots of Macs proving that a "clean" install made their Macs faster. Nothing yet. It's one of great enduring myths. And it can have significant downsides; anytime you reformat a disk and reinstall everything you're taking a chance.
And it's overkill if you do have problems. A more reasonable approach is to find the problem and fix it. Odds are it isn't the system itself that's corrupted; it's usually some software or utility or other thing you added. Better to find that problem and delete it than delete the entire disk and all your data just to remove that one offending part. The irony is people then sometimes just reinstitute the problem by copying it back, restoring it back, or cloning it back.
The way to remove bugs is to remove bugs. Of course YOU can't remove bugs in the system software because you aren't able to write it. And on occasion there's some people with a combo of hardware or software that didn't get tested with the beta ML or whatever and it just doesn't work. And since you can't usually remove chunks of the OS, you might have to go back to an older version. But even if that problem arises, a clean install won't help: putting the ML system software back will put the bugs back.
Sometimes you have no choice; disk failures, buying a new machine, etc. I've done scores of Macs and can't say that migrating to a newly installed system works any better than upgrading over the old system. But there's no reason not to try Apple's installation method: it works for most everyone, it's faster, and if it does fail, THEN you can erase everything and try over.
As long as you've got a back up you KNOW works.
Rob
