In almost every instance where a user interacts with a service, a license is at least necessary and always beneficial.

A license is a contract between a customer and a vendor that defines and guarantees what actions a grantee (e.g. a user) is able to access with a product.

Even if the product is free and doesn’t involve any form of payment, a license is still necessary for these reasons:

• Control of access. You can control by license exactly what the user can and cannot access within your product, and how much they can access. 

• Intellectual property. A license agreement makes it clear that while customers can use your service, they don't own the software itself. It helps protect your code, content, and trademarks from being copied or misused.

• Compliance. Within agreeing to a license, you can define terms of use, privacy policies, and disclaimers. This can help you manage liability and comply with regulations.

In short, a license for your SaaS service acts as a foundational agreement that protects both the developer and the user.