First question: what does the site need to tell?
If your business can be explained in a few sections — who you are, what you offer, why choose you, how to get in touch — a single, well-designed page is often the best answer. Visitors find everything by scrolling, with no menus to explore.
If you have many different services, projects to show, products or articles, each deserves a page with its own address. People searching Google for a specific service land straight on the answer, and you can explain everything without rushing.
Second question: does it need to do things on its own?
A presentation site leads to contact: phone, email, WhatsApp, a form. When the site needs to confirm bookings against real availability, give access to a private area or store and process data, you're in web app territory.
A web app is designed around the way you work and needs more analysis, more testing and more maintenance. It pays off when it replaces repetitive manual work: answering the same requests over and over, say, or managing availability by hand.
Third question: how much does it need to grow?
You don't need to build today the site you'll need in five years. A well-built one-page site can gain dedicated pages when they're needed; a multi-page site can later take a private area or a store.
What matters is that the structure starts out tidy: copy, images and data organised so that adding a part doesn't mean redoing everything.
Three concrete examples
A neighbourhood barber with a clear offer: a one-page site with services, hours, photos and a WhatsApp button. A practice with four areas of work: a multi-page site with a page per area and an FAQ. A rental business that wants bookings with an up-to-date calendar: a web app, or a connection to an existing booking service, is assessed.
- Clear offer, direct contact → one-page website
- Several services or content to be found → multi-page website
- Bookings, accounts, data → web app or a connected external service