There are two problems with this strategy, however: First is size. Boot up into Yosemite to play, experiment and test, then go back to the stable, shipping Mavericks for your production work. So yes, installing the OS on an external drive or second partition or similar is very smart. There’s also going to be all sorts of extra system logging for debugging purposes so performance isn’t going to be as snappy as people would prefer and there are issues of upgrading mailbox formats, bookmarks, preferences, etc, just to find out that if you need to back up to 10.9 Mavericks, well, you’re in a big jam.
With a public beta, it’s inevitable that people are going to leap onto the bandwagon so they can have a preview of Mac OS X 10.10 “Yosemite”, just to find that there’s a reason that “beta” is in the name at this point and have things fail to work properly or even at all.
