This has certainly been written here on HN a thousand times already, but here again are the basics for thinking about business (software or otherwise):
1. A business is not a product, project or a program. It is an entity designed to provide something people need in return for money such that the result is beneficial (profitable) to the business.
2. The question you should ask when thinking about business is “what can I provide, at a competitive price, that people (or other businesses) need to buy.
3. So why do people need things? Answer: sustenance, pleasure, efficiency and convenience, solving an important problem, or ability to make something else of value, ie. a tool. These are things that provide “value” to the buyer.
4. There are subtleties in (3) that can be exploited if you have lots of experience in a specific area. For example, a chef may know of things, tricks or tips of value related to cooking.
TL;DR In summary, it doesn’t matter what kind of product or software you are building, or whether you use a SaaS model or other business model. What matters most is that the business is designed to build something of value for lots of people that results in a healthy profit. The “idea” has to be the solution to the value problem.