Although, in many cases, the employees will be more interested in a corporate intranet which is not public facing.
As has been mentioned, potential customers. Also, existing customers looking for support - if I have an NVIDIA based graphics card, I might simply start at nvidia.com looking for driver downloads (quick check - that will get you to the appropriate area in a couple clicks).
Or, for companies which make a product sold directly to consumers through retail outlets, before going to the store or ordering online. Garmin’s corporate site is full of rotating graphics touting their gadgets, for instance.
These days, corporate web pages seem to have evolved to having a lot of “creative” puffery on the front page, often heavy on flash, videos and god knows what else, together with some sort of tabs or menu bar somewhere allowing you to get at the specific area you are interested in, such as press releases, investor relations or product information. Those things can be hard to find for companies like banks or brokerages, which use the default content displayed on their most easily remembered url as a login page for customers using their online services, and advertise a lot of products and services on that page. Try to find the corporate stuff from schwab.com, for instance. You have to look down the page to find “about Schwab” in the content, rather than actually being able to get at it through the tabs at the top.
BTW, to find the corporate web pages, rather than simply googling the company name or guessing the url, you might wish to go through one of the financial sites which usually provide links to corporate profiles. The entry for a company on http://google.com/finance, for instance, contains a “Website Links” box listing the general corporate URL, as well as direct links to “investor relations”, “products”, etc. For instance, the info on “SCHW” links you directly to “aboutschwab.com”, rather than you having to find it from “schwab.com”.