Primarily joints in precast claddings are intended to ensure the weather tightness of the building despite the movement to which they might be subjected. From the diagram below it can be seen that if any water manages to penetrate the sealant, its progress through the joint would be stopped by upward slope.
Most between-panel joints will act as movement joints. They allow the natural movement to take place without stressing the cladding panels.
In assessing the required width of a movement joint, it should be remembered that the amount of movement experienced by a joint cannot be taken as the width of the joint. It is merely the strain experienced by the sealant to accommodate the stress and must be added to the width of sealant pointing required to accommodate that strain.