Sometimes, you'll need to pack multiple files inside of a single file. Those files will need to grow, and be able to be deleted. At that point, you're asking

Sometimes, you'll need to pack multiple files inside of a single file. Those files will need to grow, and be able to be deleted. At that point, you're asking for a filesystem inside of a file. And you can literally do exactly that with a filesystem library (FAT32, etc).