When one page is the right call
If you sell one service to one audience, a one-page site removes every decision the visitor does not need to make. Everything lives in a single scroll: what you do, proof, and how to get in touch.
It is also the fastest route to being findable. A single page with a contact form, social links and a Google Business Profile covers most of what a local business needs in its first year.
The signals that you have outgrown it
You need separate pages when you have separate audiences, separate services that deserve their own search visibility, or content that keeps growing. A service page that ranks on its own terms will always outperform a section buried mid-scroll.
The other signal is sales conversations. If you keep sending prospects a PDF because the site does not cover something, that PDF should be a page.
Plan for the second version
Build the first site so the second one is not a rebuild. That means owning your domain and hosting, keeping the content in a structure that can expand, and setting up analytics from day one so the redesign is based on data rather than opinion.
Most of the cost in a website redesign is not design. It is re-deciding things that were never written down the first time.