P.S. Since 2018 Windows 10 update, OneDrive management became better and now it allows to set files on-demand (so free space on your PC) and to have different sharing options to files/folders. See, for example,  https://www.windowscentral.com/how-get-started-onedrive-windows-10

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Some time ago, in a post, I talked about the synchronization of the OneDrive predefined directory in Windows 8.1.
Now in Windows 10 the “on-line only” option doesn’t exist anymore: Microsoft removed the placeholder functionality from its OneDrive sync client. Things keeps moving very fast in OneDrive management … and this won’t be the end of the story!

I appreciated the fact that now you can decide to sync [see the following screenshots] only some directories (even though they should be the ones in the predefined OneDrive directory and not whatever, as  it was in Windows 8 if I remember well), so there is not the need to waste storage space by  smartfiles or place holders with the “on-line only” option.

OneDrive Settings

OneDrive – choose folders

OneDrive – Folders to sync

OneDrive – Get Help

So  I think that the actual solution is one side better than before (no deletion on the cloud of the directories that you do not want on your PC, so you had to have the place holder of all the dirs. if you wanted to synchronize the OneDrive dir).

However  there are unfortunately the following lacks:

• No more the possibly have an “on-line only” option as it was in Windows 8.1 (sometimes useful).
• No more the possibility to sync a generic directory of my PC (other than one available in OneDrive) [as it was, if I remember well, in Win7/8].
• No more the possibility to change the location of the local OneDrive folder … (I think there was in an initial release in Windows 10, because on one PC I have it in c:/Data but now, when I tried to do the same with an other Windows 10 PC, I cannot find anymore the way to change the default c:/Users/myAccountName folder location of the OneDrive directory).

So it would be sometime nice to have a reference to all your OneDrive files from the File Explorer (even if you don’t want to waste local disk space on your PC) in order to access OneDrive directly from apps like Word and do any other file operation you normally use.
I found in some blogs (*; **) an easy method to map your OneDrive storage as a drive and so reach that goal. You may follow the detailed instructions you can found there or simply consider the following steps that take care also of my experience and some little changes (as how to actually find out your CID):

1. Find out your OneDrive CID. To do so, ou have to go with a browser to your OneDrive site and then access whatever of your folders: in the URL you will see, as a query parameter, your cid (e.g. https://onedrive.live.com/?id=123456asdfghj&cid=1A90RA8F00049FB6&group=0) the CID in the address bar.
2. Open up Windows Explorer, select “This PC” in the left pane, click on “Map Network Drive”  in the ribbon under the “Computer” tab. In the “Map Network Drive” dialog box that pops up, select the drive letter you wish (e.g. Z:) to use for OneDrive and in the “Folder” text box, enter “https://d.docs.live.net/” followed by the CID number you retrieved in step 1 (e.g. https://d.docs.live.net/1A90RA8F00049FB6).
   

   Map Network Drive

3. If you wish the drive to be available every time you log into Windows 10, select “Reconnect at sign-in“.
4. Check “Connect using different credentials” so that you can confirm your OneDrive sign-in information, entering when requested your Microsoft credentials (be careful about possible proxy problems if you are on a local network, so better to test all connecting directly to Internet. Moreover the username should be your yourMicrosoftUsername, that is the email you used to register in Microsoft, one and not Microsoft Account\yourMicrosoftUsername, as sometimes it will be suggested if you do not save your credentials).
5. Once you’ve entered your credentials, it may take some time for your computer to fully connect and the speed of displaying the remote files on your File Explorer will obviously depend on the kind of connection you have …
6. The folder you will have in File Explore will be like
   1A90RA8F00049FB6 (\\d.docs.live.net@SSL\DavWWWRoot) (Z:)
   that it is not very nice to see!! So, you can possibly rename it right clicking on it (e.g. you can rename to OneDrive so it will be displayed as OneDrive (Z:)

After having renamed the mapped network drive Z:

As it is rightly said in one of the mentioned posts, it may be not a perfect solution and can result in some performance issues … but if your goal is to be able to access all of the files in your OneDrive cloud storage from File Explorer in Windows 10 without having downloaded in your local HD, this may be your best option! They are not anymore local thumbnail as it was in Windows 8.1, so you can see them only if you are connect to Internet … but in this way your local HD  haven’t to store nothing … so neither the space needed for storing thumbnails is lost and, if you have many photos, this could be relevant.

Therefore, I do not think this is a FULL solution because of performance problems on slow networks and because it does not allow to see your files when the PC is disconnected from Internet (while the on-line only option available in Windows 8.1 allowed that [e.g. see a picture’s thumbnail], even though if you wanted to download the file/picture you had to be connected).

I think that MS has to find out a better solution, may be adding some more options, … may be taking something from the past!

PS: see this video too!