Or, if you can't read the whole thing (it's only a few hundred words) for whatever reason, here's the thrilling conclusion:
If you like to live dangerously, go ahead and install Sierra and iOS 10 the minute they come out. I will, but remember, I’m a trained professional. So, before you do something you might regret, I’d like to remind you one more time that it’s never as easy to downgrade as it was to upgrade and if you want to regress to a previous version after an upgrade you’ll have to erase the device, reinstall the previous version of the OS, and then restore your data from a backup. Not fun.
The bottom line is that when macOS Sierra 10.12.0 and iOS 10.0 finally arrive next month, wait for the first bug-fix update before you pull the trigger. My father used to tell me, “better safe than sorry,” and when it comes to point zero releases, I’m pretty sure he’s right.
Just say “no.”
This may be the best productivity advice I'll give you all year—DON'T INSTALL SIERRA TOMORROW! While it's not likely, do you have time for this if your upgrade goes bad???
Like I said, it's not likely... but it could happen.
One last thing: You might want to read my column on beta testing operating systems: Dr. Mac's Guide to Apple Public Betas (Dr. Mac's Rants & Raves Episode 183 for The Mac Observer).
Why? Well, if you install tomorrow's release, you're basically installing a beta OS... So here's the bottom line: Installing Sierra tomorrow will probably be fine for most users... but if it's not fine, do you have time to deal with it tomorrow?
Ask yourself this: Do I absolutely, positively have to have Sierra tomorrow?
I thought not.
So, wait until Saturday or for the inevitable 10.12.1 release. You won't be sorry.