For me a clean installation means uninstall the current and install a new one or at least keep one clean copy as a backup, so that you can always go back to it when something breaks in your copy that you're actively playing.
When it's said that a new world must be started for best experience in new Alpha, the way I understand it is that I can't just try to open a save from the last Alpha with the old world, because that most likely won't work correctly in the new version of the game.
As for deleting the old worlds and/or registry entries, I never really had to do that to solve issues that I ran into. Just starting a new game for sake of testing a new Alpha was alwasys enough to avoid compatibility issues.
As for the Mods, I always create a separate copy of the whole game to play with mods. That way I can always go to my vanilla clean copy in Steam Library without the need to redownload the whole game again when something breaks. It greatly saves time, internet bandwidth and sanity of me as a player and you as moderators who would be bombed with my questions and problem reports...
I wouldn't say that playing it safe is complicated though. I mean sure, it's probably a hard task for you as a moderator to try to answer all kinds of different questions when you don't have much to go on, I can understand that, but then you will probably agree with me when I say that all users should try their best to play it safe by following these simple rules I mentioned above to help avoid running into issues and if they still run into some issues after making sure they did their best to avoid them in the first place, that'd be a good time to come here and report the problem.
