SEO Problems with Loading to a Subfolder?

[Kevin_P]

A client has a single page app website that shows https://example.com/example when you visit https://example.com . I don't think this is a redirect; I think it's a URL rewrite. My questions:

1. Is this setup common with single page apps?
2. What are the SEO benefits or drawbacks of having a domain's homepage load, rewrite, or redirect to a subfolder?