Magnetic shielding is to reduce the amount of magnetic flux generated outside an inductor, in terms of reducing the likelihood of radiating energy to nearby components or circuit board traces causing EMI. Whether a shield is necessary or not depends on the proximity of other components and how field interactions would affect the circuit's performance. Field interactions are challenging to prototyping while measurement of the final circuit design is recommended. In addition to reducing radiated fields, magnetic shielding typically helps to achieve more inductance per given size of an inductor.