Because sometimes you don't want everything in the cloud
In the desktop version of Office and in Office 365, if you are logged in using your Microsoft account, it will try to save the file to your OneDrive account by default. This is a new feature that started back in Office 2013 that aims to help you move your documents to the cloud, so that you can access them from anywhere and so that they are backed up more securely.
I think this is a great feature, but I’m not really too happy that Microsoft defaults saving of all files to OneDrive! I personally don’t want to save most of my documents to the cloud and find it rather annoying to have to keep clicking on This PC to save an Office file locally.
Luckily, there is a setting you can change so that Office will save files locally by default and if you want, you can always manually save the file to your OneDrive account. Here’s how to do it.
Save MS Office Files Locally
First, open any Office program like Word. Then click on File and click on Options.
Now go ahead and click on Save in the left-hand pane and then check the box that says Save to Computer by default.
You can also change default local file location if you like in the box below the checkbox. Now when you go to save a file, it will save it locally rather than to your OneDrive account.
The one nice thing about Office is that when you make that change in Word, for example, then it automatically changes the default save location on all the other Office programs like Excel and PowerPoint, so you don’t have to change if for each individual application. Enjoy!