Does it help with country targeting to use hreflang with only one version of each page?

So I'm working on an American website that's targeting Americans. Due to the nature of the service (legal), there's essentially zero scope to target other countries. So looking to zone in on the US as much as possible.

I'm wondering if setting up hreflang tags for en-us would help with the specific country targeting? Or would it be a waste of time, and/or hurt the site in some way?

I know usually you only generally use them if you have multiple versions of each page, so just want to make sure I'm not about to do something stupid.

Thanks