E.g. you want to access some server or services at your home, but your ISP is changing your ip address every 24 hours. With a DDNS service you can always use the same dns name, only the a/aaaa records of these will be updated when you get a new ip address from your isp.
Interesting ... any enterprise oriented use-cases ?
There are some uses cases, e.g. you have many external devices that are not having reliable internet connections and are not smart.
The real enterprise use case is rather a full dns service for domains with some additional services (that will be available soon on BlaBlaDNS ;)