Thanks for the further details. So, basically, the architecture of your website and its navigation send signals to humans and search engines about which pages you deem to be most important.
Take a look at the homepage of Moz and the main menu at the top. For example, we're linking to our blog, signalling that this is a core component of this website, but, we're not linking to every single blog post on the blog, meaning we don't consider each post to be as important as the main blog link.
Similarly, we have a link title "Learn SEO" which takes us to a page that is basically serving as a sub-menu of the educational tutorials we've developed. We don't link to each tutorial from the top level menu, but the path has been created to get there.
For a local business, the top level menu typically includes:
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Contact Us page
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Reviews/Testimonials page
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Blog (if they have one)
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Link to or dropdown for the pages that describe each of their services
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Link to or dropdown for the pages that describe each of their physical locations or service cities
At the minimum, that's what you'll typically see, but the size/complexity of the website will play a role in influencing what you put in the top level menu, with the goal being that you are highlighting the pages you feel are most important for users (and search engines) as the very top pages of your website.
To ask if it hurts you to put some pages in the top level navigation while leaving others out somewhat oversimplifies the issue. All website owners have to make these choices to prioritize what goes in the menu. It's not really a matter of being hurt - it's a matter of being sure that your core pages have received maximum prominence in the menu.
Now, if you built a page that was like an island with no path to it from anywhere in the site, then, yes, neither humans nor bots might ever find it. But, at the end of the day, a website with 20, 50 or 5,000 pages can't put all of them in the top level menu, so best advice here is to carefully, thoughtfully plan the navigational architecture of the site so that core pages are immediately accessible via the main nav, but that there are very clear and abundant paths to less prominent pages as well.
I hope digging into this a bit more this way is helpful