I see some very good points were already made, but I think UUIDs are also good for at least three other reasons: 1. Offline / sync - you can have out-of-sync o

I see some very good points were already made, but I think UUIDs are also good for at least three other reasons: 1. Offline / sync - you can have out-of-sync or offline clients (e.g mobile apps) inserting new data without worrying about pk mismatch or collisions. 2. security - it's obviously a bit of security through obscurity, but not being able to guess the key of an object can be very useful some time. It shouldn't be relied on as a first line of defence, but it gives you a naturally impossible-to-guess reference. If you want to avoid someone crawling through your image-base or any object that is generally accessible, but you want to avoid having it accessible in-bulk, UUID is your friend. 3. Silly mistakes - If you pass an object id, you really want to know it can only be for one object. Maybe the front-end is sending an id of one object, but the backend is working on another (shit happens). When you use sequential ids, you increase the chance of weird stuff going on. With UUIDs you simply can't use the wrong id, even by mistake.