[avmich]

We can talk about even more general idea of saving file space: compression. Ever heard about it used across the whole filesystems?

[fh973]

Most compressible file formats are already compressed, and with compression you lose efficient non-sequential IO.

[praseodym]

Microsoft MS-DOS and Windows supported this in the 90s with DriveSpace, and modern file systems like btrfs and zfs also support transparent compression.

[eeeficus]

You introduce overhead on both read and write without being a better solution to OPs problem.