Why is a SaaS financial model different from a product-based model?

SaaS (Software as a Service) allows a user to use the software without owning it. In a product-based model (eg. Microsoft Excel), users purchase the product and then are responsible if something goes wrong or breaks down. Additionally, they need to purchase a new one in order to upgrade. With SaaS the company handles the software, fixing and upgrading as necessary, and the customer purchases the right to use the software. Instead of selling to the customer a product, SaaS sells the service that the product performs. In addition, SaaS models ensure business continuity, protecting you from losing your files if your computer crashes.