Thank goodness I don’t have Win 10. 
Me neither, but I’ll be hard to avoid once I finally set upon a PC upgrade
… my win7 looking mighty good right 'bout now 
srs hope this/MS doesn’t cause any of you any severe trouble 
Why people even place stuff like photos, videos, music, Pr0nz and other important things in “My Documents” boggles the mind. So are people too damn lazy these days that setting up partitions and your own personalized folder structure setup something they don’t even bother to do? Good thing I’ve common sense to not just put things where Windows recommends me to place them in. Screw you Microsoft 
This case seems to be selection-al and doesn’t happen to everyone. I’ve been past this update as I have the insider build.
Don’t assume people to have the same level of knowledge that you have, and never assume that just because something is so simple, it actually is, and for a lot of people a computer is a commodity, placing things where the system recommends you to do it is to be expected.
Unless of course, I’m missing the joke here, I have a hidden record of doing such
and also from reading a thread on Reddit with some people there whole windows profile got deleted so it’s not just stuff in “My Documents”.
What’s not simple about creating your own folder structure?
Open windows file explorer, navigate to a directory of your choosing, right click and select “New Folder”… easy peasy doesn’t even take five seconds to do so.
RFE: Addendum.
Good thing Microsoft currently halted the automatic insertion of the update for now until things get sorted 
I’m on W10 Pro and I’m using the business update branch so that I don’t run into this kind of issue which is nice
My stuff is all in My Documents. Why? Duh, because they’re my documents!
Well my stuff is in… My Stuff
And my documents are in My Documents, my music in My Music, my videos in My Videos, my photos in My Photos and my Pr0nz in… My Secret Stash
The way people organize their own files is a matter of personal taste, not subject to your judgement on people’s motivations and intelligence. It’s quite possible (and reasonable) for a person to have multimedia projects sorted by topic rather than medium. For a 3D model, I will have CAD documents, images, text files, links, etc. all residing together because they’re describing the same object.
What actually is common sense is to keep at least one backup on a drive that is not your boot drive. As long as you do this, your important files are safe from a multitude of possible negative events, and there is no need to wonder if anything happened to them without you knowing it.
This!
Additionally, it’s good to have a Linux partition even if you are doing all your work/gaming on Windows.
Seriously, Linux saved my ass about a million times because of the retarded “permissions” BS Windows has. If your Windows partition ignites in flames 
(not literally, but if the updates doom it to hell) you can always acess your Windows files through your Linux partition or boot CD. 
Not everyone knows that it’s totally safe to make your own folders on the root of the drive, so long as you don’t touch anything else, in fact, not many people dare to go beyond that “don’t touch shit inside here if you know nothing about it” screen.
And there’s nothing inherently complicated with it, but it’s even simpler to just, you know, use the default recommended folder.
I agree with @BlivetWidget, your best approach would be to make backups of the stuff you can’t totally afford to lose somewhere else besides that machine.
Maybe we should discuss backup software. Like many computer activities, choosing backup software ends up creating a barrier to entry for a lot of people. There are so many options out there, with wildly different behaviors, because we aren’t all looking for the same thing. My parents need something that “just works” in the background. I need something that let’s me micromanage. So I’ll start the discussion with what I use:
What: Unison
Where: Unison File Synchronizer
Pros:
- GUI or command line, as you prefer
- Makes no assumptions in the case of a file conflict (prompts you to choose).
- Considers all locations equal (aka no master. This means you can change a file in location A or B and it will propagate it to the other. Especially handy when the “backup” is less of a backup and more of a travel drive).
- Extremely fast after the first run (the default mode basically builds a file list for each directory, which is how it knows when things change), because the backups are incremental.
- Related to the above, propagates deletions (some backup software only compares modification times and therefore assumes an existing file takes precedence over a non-existing file).
Cons:
- Requires some savvy to set up a profile correctly (profiles are set up in text files).
- Lives only in the present (there is no history, and no going back to previous editions of a file after it has been overwritten by the latest backup; there is only locations A and B). This is not a con for me, but I know it will be for some.