What is it for and can i run a zetec without it. (see pic below for example)

According to Mr Haynes the primary function of the valve is to raise the exhaust gas temperature on start which reduces the time taken for the lambda sensor and cat to come into operation. Once the engine is at normal running temp it is isolated by the ECU through the pulse air solenoid valve.
I don't intend to use it.

Mick