You have a vision for your product. You want to design and build the best possible user interface for your product but you can't find an off-the-shelf board that lets you get your connectors where you need them, or maybe you need to include some specific (non PC) connectors. You are talking extra cables, riser cards - complicating your design and adding cost. Or you can compromise your vision.

Or you can look at using a COM (Computer On Module) board.

Think of a COM as an off-the-shelf building block with all of the functionality if a typical single board computer - CPU, main chipsets, RAM etc but without the usual IO connectors eg: PS2, D-type etc. Instead the COM plugs into a custom host board using defined interface connections.

The host board footprint, connector layout, GPIO and any application specific electronics are all tailored to your target application. So you have a standard OTS core module and your custom host board is simple, cost effective build. Bring them together and you get the custom solution you need, the footprint you need, the connector lay out you need - at a cost you can afford.