File Exclusions: Compressing a .mp4?

[elliotmarks06]

Why are there so many file patterns to exclude from compression? What would happen if I tried to compress something like an image or an mp4? I know that I can do video compression in handbrake, but I just wanted to know what compactor would do to it.

[Dr-Emann]

Because mp4 files are already compressed, it is very unlikely to be able to meaningfully compress them further.

[Freaky]

It's just a performance feature - as @Dr-Emann says, MP4s and the other types in the exclusions are already compressed and are unlikely to benefit from the attempt. Compactor shouldn't really do anything different without the list other than take longer and churn the disk more.

There are a couple of safety exclusions in there too - the Windows folder and special NTFS folders, just as an extra layer of anti-foot-shooting beyond the system file flag check and NTFS permissions.