For anybody that doesn't want to use the workaround developed by dropbox, as this removes the ability to see the size of the file that you are about to download, you can create a Sparse Bundle using mac's Disk Utility. This will act as a thumb drive/external hard drive, but its housed on your mac. This also removes the logical size taking up space, but you can still use its information to make informed downloads (this is very important if you are a video editor w/ limited space)
Here is a tutorial on how to make one. ( I set the size to 100 GB, but you can set it as high or as low as you want. Some people may only need a max file size of 25 GB.) It is important to set a limit that is less than the size of your hard drive.
Once made, change the location that you sync your files to.
Hope this helps!
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