Of course, just as you need to sell it to make any money. I was talking about "marketing" and "sales" as in department sense, so what I want to say that you can run a company with just engineering department, but you can't run a company with just sales and/or marketing departments (in a product orientated business at least). Sure, it's probably not the most efficient way either. For example, in my previous job I was working in a small, niche company (optical equipment) that had only engineers (~40 total), CEO and an accountant and it was doing pretty good, we had hard times fulfilling all orders. All "marketing" we did was our CEO + few engineers going to the industry related conferences and shows to generate leads.