To give you an example of where this is used, have you ever seen this website?
MineCraft uses procedural generation for its worlds. Every time you create a new world, you are given the option to enter a seed, or leave it blank. If you leave it blank, the seed is randomly generated. If you enter a number, the world generated from the number you enter will always be the same, so that's kind of a way of sharing worlds with your friends.
"Windows 10 doesn't only include spyware, it is designed as spyware" -- Gaius Publius, The Big Picture RT Interview
"[...] we will access, disclose and preserve personal data, including your content (such as the content of your emails, other private communications or files in private folders), when we have a good faith belief that doing so is necessary" -- Windows 10 Privacy Statement