Package files are a handy way of sharing files between different computers and/or designers and maintaining the file structure.
If you just zip all the part, assembly, and drawing files that may work for you. But if you have hardware that comes from a location other than that of the model you then need Package to pull in all the hardware. When you unpack the assembly the file structure will be recreated, including that of the hardware.
I suppose you could put all the hardware in the model file location, but that could end up duplicating your hardware.
Also, If you need to provide a file to Support for assistance, then a Package file is the quickest way to create a file for uploading.
These are examples from my experience.