Renting means the panel engine, the server and the updates stay with the service, while the business is entirely yours: your domain, your brand, your catalogue, your prices and your customer base. There is no licence to buy, no VPS to provision and no developer to hire - the panel already runs, and selling is what is left for you.
Against buying a script the difference is where responsibility sits. A script hands you source code and, with it, hosting, SSL, updates, attack protection and debugging somebody else's code. In a rental all of that is part of the service, and you pay for the volume that actually went through the panel.
Against a child panel the gap is wider. A child panel is tied to the parent's catalogue and prices and works with exactly one supplier. A rented panel lets you connect any number of provider APIs and move a service from one supplier to another the moment quality slips.