Two different jobs
When someone searches for a dentist, a barber or a plumber near them, Google shows two things: a map with a few businesses pinned, and a list of websites. Your Google Business Profile is what gets you onto the map. Your website is what happens when they click through, and it is also part of how Google decides who goes on the map in the first place.
Owners often treat them as alternatives. "I have a Google listing, do I need a website?" The answer is that they do different jobs, and each makes the other work better.
What the profile does
The profile is your entry in Google's directory of places. It carries your name, address, phone, hours, category, photos, reviews and a link to your site. It appears in the map results and in the panel on the right when someone searches your name.
It is free, and for a local business it is the single highest-return listing there is. Reviews accumulate there. "Open now" comes from there. Directions come from there. For a customer who already knows you, or who is choosing between three pins, the profile can close the deal without a website visit.
What the website does
The website is where the profile cannot go. It explains what you actually do, for whom, at what price. It shows the team and the place. It takes the booking, with a deposit, into your calendar. It answers the questions the profile's short description cannot. And it ranks for the searches that are not "near me": "invisalign cost", "physio for runners", "emergency plumber weekend rate".
It also feeds the profile. Google uses the website to understand what kind of business you are, whether your details are consistent, and whether you are legitimate. A profile with no website, or one linked to a dead page, ranks worse on the map.
How they feed each other
Consistency. Name, address and phone should be identical on the profile, the website and everywhere else. Not similar. Identical, down to the abbreviation of "Street". Inconsistency makes Google less confident about which business is which.
Categories and services. The profile's category and services list should match what the website's pages say. A profile listed as "Hair salon" with a website that talks mostly about lash extensions confuses the signal.
Hours. Set them on the profile and mark them up on the website so Google can read both. When they disagree, customers arrive at a closed door and leave a review about it.
Reviews. Ask for them on the profile, because that is where they count for the map. Show them on the website, pulled in automatically, because that is where they persuade.
Booking link. The profile has a booking button. Point it at your website's booking page, not at a third-party marketplace, so the booking lands on your domain and in your system.
Photos. Upload real photos to both. The profile's photos appear in the map panel; the website's photos convince once they click.
The mistakes that cost bookings
A profile with no website link, or a link to the home page when there is a booking page. Every extra click loses a share of people.
Letting the profile lapse. Unanswered reviews, old hours, a photo of the previous owner. The profile looks abandoned, and the map result suffers.
A booking button pointing to a marketplace. Fresha, Treatwell and their peers will happily take that traffic. The booking should land on your site first.
Different phone numbers. A tracking number on the profile and the real one on the site, or vice versa, splits the signal. If you use tracking, use it consistently.
Ignoring the Q&A. People ask questions on your profile. Unanswered, they get answered by strangers.
A monthly ten minutes
Once a month, open the profile: reply to new reviews, check the hours, add a photo, glance at the Q&A. Then open the website's hours and prices and make sure they match. That is the whole maintenance. On a care plan we do the website half and prompt for the profile half.
Where the website earns its keep
The profile brings the click. The website converts it, and it does so for the searches the profile never sees. A business with a strong profile and a weak website gets found and then loses people at the door. A business with both, kept consistent, gets found and booked. The Essentials package is built around that: hours and location marked up for Google, a booking page for the profile's button to point at, and the same name, address and phone everywhere.