Other types of B2B companies also have to sell, but SaaS companies are pretty unique due to their zero marginal cost of sales. Physical product companies have to sell AND buy inventory in order to be able to sell more. Services companies have to sell AND hire and train more billable employees in order to sell more.
Sorry, I meant cost of goods sold, as the other commenter noted. We're in agreement: basically the entire cost to grow revenue is selling expenses because the main function of a B2B SaaS is sales.
