Does a Zip File Reduce File Size?

In most cases packing or archiving with zip / arj / rar / 7zip / bzip / gzip reduces the space used by the file. Actual file size (after decompression) stays the same.

But according to Pigeonhole principle there should be files when compressed you won’t get any space reduction.

Photos represented in JPEG format and most video formats are also pretty well compressed to start with.

However, making a zip (or other type of archiving) archive out of a number of files still has the virtue of giving you a single file to move your stuff.