Without much context I'll respond very broadly... :)
If you have content that doesn't change during a user's visit, you don't need an SPA you need a website. This is particularly true for small websites like your classic business brochure site (sites with basic contact details that are often just a hub sending people to social media accounts that non-technical staff can manage), where a blog or light, fast-loading static site will be more reliable and cheaper to maintain.
If you have an application with a highly dynamic user interface, where the user wants to see lots of quick updates without whole page reloads, then you probably want an SPA for the immediacy of the experience. This is particularly true where the business is heavily reliant or entirely based on the app; and there's a dedicated team for building and maintaining it. Still, if you can make a traditional server-side app load fast enough you can get away without an SPA; it's not mandatory.
Very large websites sit somewhere between these two... so an SPA might be right, it might not. Comes down to the team in that case.