One advantage of NTFS drives is the compression settings...

You can either set the whole drive (not recommended for a system drive) to be compressed, individual folders or even individual drives.

So yes, the drive could conceivably hold a lot more, but it depends upon the files. MP3 and JPG files may already be as compressed as they can go, for example. WAv and BMP files could be reduced by as much as half. A wild generalisation, but it's impossible to be more accurate.

Beware, though, that some system components don't like to be compressed, or have their dependent data compressed. I once fell foul of this with Microsoft Exchange... it had been running on the server quite happily on a compressed drive until an update was applied. The update installed without issuing any warnings, then Exchange died...!! Fortunately I was able to get it running again by deselecting the compression - after I discovered that it was a known issue. The new version of Exchange didn't like compressed data...

Anyway, on an NTFS drive you can select the file or folder properties, click on the 'Advanced' button and select 'Compress contents to save disk space'. Be warned, though, that it could take some time to complete!

Once completed, you'll see how much space has been saved by looking at the folder properties - it will list the actual size and the 'size on disk'. These may well already be slightly different without compression, but you should see a marked difference if the files are compressible.

I tend only to compress archive data, driver archives and the like, as compressing an executable or current data can slow things down a little, or even a lot!