Run an e-commerce site, and the need for product pages is pretty clear. If you don't have pages dedicated to the items you sell, your customers have nothing to put in their shopping carts.
But if you run a more esoteric business, it's harder to see why those product pages are so critical.
For example, imagine that you run a hair salon. You offer plenty of services, including haircuts, color, and permanents. Technically, all of those things are products. But when people come into your shop to visit you, conversations don't revolve around those products. You don't open up the talk with the client's need for a clip, clean, and color. You let the client lead. You talk about famous people and how they look. You ask the client what he/she is feeling while looking into the mirror. You offer to help, not push a solution right away.
Marketing companies often feel the same way. They may offer SEO, PPC, social media monitoring, and reputation management. But the sales staff opens conversations with discussions of revenue, perception, and market share. Products enter the conversation last, and only after the salesperson has a good grasp of the client's market.
Let the sales team drive your marketing strategy, and you'll have a website with no product pages at all. Instead, you'll have materials that emphasize your ability to listen, customize, and solve problems.
What's wrong with that? Plenty.
Google needs product pages to understand what it is that you do. If you offer Spanish language classes and translation services, but your corporate website doesn't mention those products specifically, Google doesn't know when to surface your site in search results. When people search for "Spanish language help near me," you probably won't show up.
Let's take it one step further.
Imagine that you want to create PPC ads that highlight your work. As a salon owner, for example, you might want to offer a discount on first-time haircuts. But as a product-averse person, you don't have any product pages that discuss your haircutting ability. And you might not let your team mention haircuts in your PPC landing page.
You can imagine how well this works. Best case, you waste money and get nothing. Worst case, you're slapped with a keyword/destination mismatch from Google, and you're banned from running similar ads.
I understand that sales teams are shifting their approaches. (I've read The Challenger Sale myself, although I wouldn't recommend it to anyone else.) It's vogue to discuss "solutions" and "conversation" instead of "product."
But if you're planning to do anything in the digital sphere, those product pages are required. Never forget that.