Building single site from a monorepo

I have an additional question to the documentation on building from monorepos.

What happens in case I have multiple sites setup to host on Netlify, but only one of them has changes inside the repository. Do all the sites that are configured to build with Netlify then get built, or only the one with actual changes inside the repo?

Yes, all sites connected to the same repo will build. But this is when the ignore script comes in handy:

Right. Clear, thanks!