Pin outs are the information on what every pin coming into and out off the ecu is and does allowing you to take it from the donor and run it in a project. Anything from a boat to a plank of wood.
So you can run an engine on the factory map at very little cost. St170 or zetec for a tenner plus your time. Or say omex or megasquirt plus loom plus mapping. Circa £1500.
The trade of is power against cost.
Turbo zetec on Focus Rs engine management.
Rwd St170
And I've done several others.