Most diesel chips work by either increasing the pressure in the fuel rail, or by increasing the dwell time for each injection (or both). Yes they do work and are more effective on diesel engines, because diesels are a lean burn engine - ie more fuel = more power, where as petrol engines (should) run a stochimetric burn, ie ideal air fuel ratio.
However you reach a point where the extra fuel, which also means extra heat and combustion pressure, where you risk melting a piston or cracking the head under load if overdone. There is also a school of thought which says that constantly running a higher rail pressure can damage the injectors over the long term, and decrease their lifrspan.
The standard settings are a trade off between performance and longevity, if you change one side of the equation you must balance the other side.