The power of adjoint optimisation is that the computational cost of the optimisation is almost independent of the number of design parameters. Thus, hundreds or even thousands of parameters can be used with relatively little increase in cost. But how much benefit does this provide, and is it always beneficial to increase the number of parameters? This work investigates the benefit achieved during the optimisation of transonic fan and compressor blades using various resolutions and layouts of Free Form Deformation grid. A method to constrain thickness throughout the blade span (to maintain mechanical integrity) during the optimisation is implemented and the effect of constraining thickness on the resulting blade designs demonstrated. It is shown that increasing the number of parameters generally leads to improved optimised designs, but that increasing the number of free-form parameters in the axial and circumferential directions is more beneficial than increasing the number of radial control parameters.