Businesses without systems don't scale. They also don't sell. And they burn out their owners in the process.
When the business lives in your head, three things happen. First, you can't take a vacation without work piling up. Second, you can't hire anyone effectively because you have nothing to train them against. Third, you can't sell the business because the buyer would be buying you, not an asset.
Systems solve all three. Written procedures turn your knowledge into training material. Documented processes let you hand off work without breakdowns. Measurable workflows let a buyer see exactly what they're getting.
If you can't describe how a task gets done in your business without mentioning your name, you have a system problem.