Consider what will happen if for any reason an error persists in a controller measurement. A simple integral action integrator would just keep on building up to a larger and larger value. If later the measurement error is removed, the integral is still there and will take about as long as the original error persisted before it unwinds back to a sensible value.
To prevent this happening. the size of the integral has to be limited. Either an arbitrary maximum may be set, or else integration may be turned off in certain circumstances. These would typicaly be when either the measurement or controller output reach the limit of their ranges.
The phenomenon is called windup , and the solution anti-windup